Changed the wrist pin on my MM5 5 Port tonight. It is the original pin and had done 115 tanks, so just over 3 gal.
It was in pretty good condition. Didn't have to forcibly tap it out, but it was a snug fit and required being pushed out to remove it.
Both ends and the middle section where the rod sits measured 3.98 mm, so only .01 mm of wear over 3 gallons.
The new nitrided pin measured 3.99 as per factory specs, and was a snug fit, so piston etc looks to be good. Double checked the clips were seated fully with the aid of a x12 magnification jewellers monocular. These are only about $20 and a great tool to have for checking things like this. Just gives you peace of mind - especially when your getting a little older and the eye sight isn't quite what it used to be I would recommend getting one if you don't already have one. Just ask your local jeweller where they get their tools etc from.