Anyway, i have carefully (and successfully) driven the roll pin out of the headstock lock (part 72) but I can't budge the lock off the shaft.
The machine was made sometime in the mid to late 80's (serial no. 020889 and reading the list of numbers I see more than one possible year). It was build as a 510 and I upgraded it to a 520 after I bought it last year, from the original owner. My best guess was the unit had seen 10-20 hours of use (50 max). The owner said it had been stored most of the time. What little use it had seen was a bit scary - a nice "scar" on the fence, and not one adjustment in the set up was even close to square or true. I'm not sure what the stains on the tables (and the band saw) were but they came out with the right cleaner. I'm guessing he may have abused the machine (over torqued the locks, etc.). I've used it lightly for about six months after cleaning it from top to bottom, lubricating it, upgrading to the 520 fence system, and doing a thorough set up.
I'd had no problems until this afternoon. I was switching from the drum sander to sawing and I noticed the headstock was a bit stiff sliding on the way tubes. The lock had turned normally several times earlier today. The stiffness should have been a red flag but I chalked it up to the crappy condition of the tubes when I got the machine (not a basket case but some rust on the bench tubes and "gunk" on the way tubes). Everything shines now and is kept waxed - so it shouldn't have been a problem. Anyway, when I went to lock the headstock, the lock wouldn't turn.
So - any ideas how to either unfreeze the front wedge or remove the locking wing now that the roll pin is out? Either one will put me one step closer to having a working Mark V.