All TenTec PTO's need to be cleaned and re-lubricated occasionally, and that job is the same from one TenTec rig to the next. But getting the PTO out of the radio is the interesting part, and it's not always obvious how to do it with minimum disruption to the rest of the radio. Here's how I got to the PTO in my Argosy 525...
Before you grab the Allen wrenches and the screwdrivers, I'd suggest getting a soft towel to set your Argosy 525 on to keep it from getting scratched as you flip it around.
1) Tune the dial as low as it will go. This will come in handy when you're reassembling the radio.
2) Remove the bottom cover (2 screws on each side, plus 1 along the
back edge, and one in front of the speaker grille - for a total of 6
screws). 
This is where I dig out some small containers to put parts in. I've got some old Play Dough containers left over from when my kids used them. I put a piece of tape on the container, and label it "Bottom Cover". That way, I'll get the right screws back in the
right place.
3) It's too bad every TenTec radio doesn't have a plug for the speaker wires; that would be very convenient at this point. But, since there is no such connector in the Argosy, I unsoldered the speaker wires at the phono jack. Before you unsolder the wires, make a sketch of where they go so you get them back in the right place. (As an option to unsoldering the speaker leads, you could remove the speaker grille and the speaker from the bottom cover. But then you'll have a speaker dangling from the radio. I prefer the unsoldering approach.)
4) Remove all the knobs. You'll need one size Allen wrench for the Mode and Band knobs, and another size for the rest of the knobs. Sorry, I didn't note the sizes. Maybe you can help me fill in this information.
5) Remove the green felt pads on the PTO shaft (there were two pads on my rig), and then carefully pry off the metal dial skirt with your finger tips.
6) Remove the front panel (4 screws). Be aware that the S-meter is loose, so don't let it drop out when you remove the panel. It's OK to let the meter hang by its leads because the leads are quite short. The ALC LED has a socket that may or may not come out when you remove the panel. Disconnect the ALC LED if it doesn't self-disconnect.
7) Take a break and make a sketch of the inner front panel, showing the positions of the dial, tensioning adjustment, and the path of the dial cord - just in case. Personally, I prefer the sketch because it forces you to notice details that might not show up in a photo. No harm in doing both.
8) Remove 1 turn of the dial cord from the PTO shaft, and tape the cord to the serrated tensioning wedge. Now remove the knotted end of the dial cord from the pin on the PTO shaft.
9) Remove the left PTO screw (as viewed looking at the front of the upside down radio).
10) Tape the stretchy cord to the right of the PTO shaft to the inner front panel (see photo).
11) Remove the right PTO screw and lockwasher on the front panel.
12) Turn the radio right side up, remove the top cover (4 screws), and locate the IF/AF Board (it's the large board, in front). Remove the (5) screws holding this board. You'll have to remove the crystal filter to get to the screw in the corner.
13) Lift the IF/AF board up enough to get to the third PTO screw on the chassis. Remove this screw, and let the IF/AF board settle back down.
14) Make a sketch of the PTO wires, then unsolder them from the PTO box.
Now you can remove the PTO.
From this point, you can follow the directions on the TenTec PTO Rebuild Sheet, or refer to K5ESE's (formerly N5FC) excellent article "Rebuilding the Century 21 PTO/Veneer". You can find this at http://www.io.com/~n5fc/ c21_pto.htm. Or, you can follow my less-detailed description below.
15) Remove the bottom cover of the PTO.
16) Very carefully remove the pin from the tuning shaft in front of the PTO box, and put it in a container labeled "PTO Parts".
17) Remove (2) screws from the black plastic bearing on the rear of the PTO box. There will also be one or two pairs of flat washers between the plastic bearing and the box. Remove these also. Put these parts in the "PTO Parts" container.
18) Remove the spring and washer that come out with the plastic bearing. Remove the washer remaining on the PTO shaft. Put these in the "PTO Parts" container also.
19) Push the tuning shaft toward the back of the box to remove the plastic beveled washer and the stop pin. Put these with the rest of the PTO Parts.
20) Clean the parts in mineral spirits and lubricate with White Lithium Grease. Other lubricants (Mobil One Synthetic Grease, Bicycle Grease, etc) have been used for this, but I prefer the White Lithium Grease because it's not as thick as some of the other greases which results in easier tuning.
21) Reassemble the PTO, applying lubrication on all bearing and sliding surfaces of the tuning mechanism.
22) Reinstall the PTO, reconnect the wires, remount the IF/AF Board, and reinstall the crystal filter.
23) Reinstall the pin on the PTO shaft, and reconnect the dial cord.
24) If you're interested in eliminating the sensitivity of the tuning knob to hand capacitance, now is the time to fix it. See "PTO SENSITIVITY TO HAND CAPACITANCE" in the Projects list.
25) Now is a good time to check the calibration of the tuning dial because you can move the pointer a small amount to make the correction. See the TenTec manual for details.
26) Reinstall the ALC LED, place the S-meter in its proper position, and reinstall the Front Panel.
27) Reinstall all the knobs. (If any of them are "mushy" , see my fix for that, "TenTec Mushy Knobs" in the Project list.)
28) Reinstall the top and bottom covers.
Your Argosy should now tune as smooth as silk, and the White Lithium Grease will be good for many years.
If you find any errors or omissions in this procedure or have any suggestions, please send me an email. I'll revise this document as soon as I can.
72/73,
ed - k9ew