True...but your next lens may have problems, too.80 bills isn't bad - but I can buy a replacement for the same price...
There use to be an *Bay seller with the handle of 'nikondave' that sold illustrated/breakdown repair manuals for all kinds of cameras and lenses; including Mamiya TLR cameras and lenses.
Also, along with Flutot's, (mentioned in post #2), for shutter repairs, apparently Mamiya USA (MAC), sold all/most of their remaining Mamiya TLR parts to KEH Camera, in Georgia. KEH may end up being the last bastion for Mamiya TLR repair, simply because they now have all of the remaining factory supplied repair parts for these cameras.
Unfortunately, they won't sell the parts individually.
They only use the parts when repairing lenses and/or cameras sent into their repair shop.
Another age related problem you're facing is your "Seikosha S" model shutter.
Those shutters were in the earliest lenses commonly called the 'Chrome' lenses.
There hasn't really been any parts available for those lens shutters for quite some time.
If you do opt for purchasing another lens, try to get a 'Black' lens, preferably one that has a 'Blue-Dot' on the shutter cocking lever.
Picture comparison example...Old 'Chrome' lens on the left,
Newest 'Black-S' lens, w/the best muti-coatings of any Mamiya TLR lens on the right:
Below, are examples of the three (3) different generations of the 'Black' series of 80mm TLR lenses.
First-production, Black, 'Plain-Dot' 80mm TLR lens:
Mid-production, Black, 'Blue-Dot' 80mm TLR lens:
Newest/last-production, 'Black S - Blue-Dot,' 80mm TLR lens:
*Note: This latest 'S' series 'Blue-Dot' lens is easily identified by the absence of any lens markings around the lens face.