Mamiya M645 Film Advancement Issue

Hey guys, I've recently acquired an old Mamiya M645 (my first medium format camera). Upon loading and attempting to take a few test shots with it, I discovered that there seems to be an issue with the film advancement.
The camera will crank up to frame 1 (I believe it advances that far correctly, at least), but when cranking it the second time, the frame counter does not change; it stays on frame 1. Something similar to this continues on throughout the roll of film. I will put a chart or list of some sort at the bottom of the post to explain it better. Now.. when I was taking the test shots, I had cranked up to the first frame, took a shot, then the camera just cranked all the way up to frame 15 and filled the take-up spool; no shutter was cocked (after the initial frame) or anything.

This does not happen when there is no film in the magazine. When there is just a magazine with the take-up spool in the camera, the advancement seems correct as far as I can see. It takes 2 complete revolutions per frame; the first revolution cocks the shutter, and advances the film. The second does nothing as far as I can tell (I have cranked the camera with the back open, holding the little switch on the right hand side in with a bank card, and the second revolution has done nothing at all), but the shutter won't fire without completing the second revolution.

I'm wondering if anyone has any idea as to why this might happen. Is it an issue with the magazine? Is there a spring or lever of some sort that needs to be repaired? Has it happened to anyone?
Thanks for any help in advance.

1st crank > frame 1
2nd crank > frame 1
3rd crank > frame 2
4th crank > frame 2
5th crank > frame 3
6th crank > frame 3
7th crank > frame 4
8th crank > frame 4
9th crank > frame 5
10th crank > frame 5
11th crank > frame 6
12th crank > frame 7
13th crank > frame 8
14th crank > frame 8
15th crank > frame 9
16th crank > frame 10
17th crank > frame 10
18th crank > frame 11
19th crank > frame 12 (half way through the crank, the end of the roll comes off the feed roll and it then advances)

i was going to ask if the little lever for multiple exposures was clicked over, but I don't think so. Sounds to me as if there is a mechanical problem.

I've made sure that it isn't set on multiple exposure. It seems as if this only happens when there is film running from the feed spool to the take-up spool. I have placed a full roll on both the feed side, and the take-up side( at separate times, NOT being run across the pressure plate); it has worked correctly. Immediately after, I put a roll in, fed it over the pressure plate and put the tab into the take-up spool, popped the magazine in, and the issue returned.

So... The issue is coming from something on the magazine, I'm not quite sure what though. I have found a video on YouTube where the issue the man had was with the rubber roller( tensioner) in the centre of the magazine that runs to the counter gear; it was something about the rubber going hard or being too tough to work properly. Once again, I'm not quite sure.

The actual counter gear in the camera is kind of loose, but it functions correctly when the film isn't fed over the plate, which again leads me to believe there is some issue with the tensioner.

Do you have another film insert (referred to above as a magazine) that you can try?

And which version of the camera do you have - initial M645, M645j, M645 1000s, one of the later model 645e, Super, 645 Pro, 645 Pro Tl or?

The inserts are quite inexpensive on the used market.

What is your location? There may very well be another APUG member nearby who has an insert you can try.

Try another 120 insert. If you still have the issue it's time for a CLA.

I've got the initial M645, and unfortunately the used photographic gear market in my area isn't too good (I'm located about 40 or so minutes northwest of Peterborough in Ontario, Canada), so I've had to order another insert (it should be here next week).

Just an update on this...
I received the second insert, the problem was still there so...
I have ordered a parts camera, and replaced a spring that leads to the frame counter, as well as the timing gear that leads to it. This has fixed the issue at this point. I'll update the thread again once I get a roll of film through it and get around to developing it. I also ran into an issue with the electronics, but that was entirely my fault for tinkering where I shouldn't have been tinkering (got it all fixed though).