I picked one up on CL last year for $50, had poor compression. Put a new ring in it and love that saw! Got a new chain and use it all the time. It's so light compared to my 394 and it seems to never get dull! The chain don't get loose, and it's not tiring to run. I cut up a ton of wood last summer that was 16" or so, and it just ripped. I did get a new cylinder and once this gets poor, will replace it but I sure love my 51. Then the 394 gets a lot less reps, and I use so much less gas also. Can cut for 30+ minutes without a fill. The 394 slams a tank in 20 or less...
Anyway, great size saw...just love mine.