Cant hold timing - possible problems?

[PHOENIX]

1983 C10 w/ 350
Still has damper from 305 (at least 16 years old)
Dist. is Proform (just under 5-years old) w/ msd module and msd coil, everything else is as the proform comes.
Plugs and plug wires are not very old.

I has discussed this before. Well I havent played with it much, but the timing wont hold, its keeps changing on its own.

The dist. clamp is solid and has not let up and I cant turn the distr. by hand without loosening the bolt, so I know the distr. is not slipping and turning.

Ill set the timing and idle, after full engine warm up and with vacuum advance disconnected. Then I drive it around for a little while and then I check the timing again and its changed from 8 BTC to 12 BTC. If I dont mess with it, it continues to get worse. We have discussed the fact the the damper may be slipping. Because in the past the timing was way off yet the truck didnt run as bad as it should for timing that far off. I got under the truck and tried to turn the damper outside by hand and it did not budge, it was solid.

I did however notice that when I rev it kind of fast, quick short burst, there is a slight tick sound that comes from the distr cap area. It is just one little tick, it is NOT continious. I was able to track this sound down with my stethescope so I am pretty sure thats where the sound is coming from. I could not hear the sound on any other parts except the distr. cap and the metal base the cap sits on. I could not hear the tick when listening to the distr. shaft (leading into engine). Is it possible something is wore out inside the distr. and causing this problem?

When you rev up an engine the timing mark is supposed to return to the proper setting right away, right?

Well mine is slow and doesnt go back to where it was before you reved it up. I have a little video here that shows what I am talking about. It is sometimes more drastic then in this video. The timing in this video is at 12 btc, last time i adjusted it I set it at 8 and it changed itself to 12 in just 15 miles of driving. I didnt bother to adjust it back to 8 before this video. Note how slow the timing mark returns after I let off the throttle. When I set the timing at 8 and rev it like in this video it slows down around 12 and slowly returns to about 10 or so but doesnt seem to go back to 8. If I have time tomorrow Ill set the timing back to 8 and shoot a video of it this way too. Also the timing light is working properly, but for some reason the camera didnt like the flashing light and would stop the light flashing on the camera, not sure what the deal was so dont pay attention to the inconsistant light flashing, just watch the timing mark and listen to the engine.

BAD TIMING VIDEO 3.7MB-14 sec.

What the hell is going on here?
Its driving me crazy. What do I change the distr. or the damper. When I open up the distr. what do I look for as far as wear? Any and all help is appreciated.

Thanks, Eddie