555/562xp MY changes, looking for a used saw

[mbrick]

Hi,

I'm looking for a 555 used or new.

Looking at a few used saws now: what were the changes over the MY's (model years)? Are there better/worse years to have? Steer clear of pre-xxxx, etc? Decomp valve, carb revisions.

The one I am looking at has non-flippy caps which I take it is an identifier of a min age, still waiting for serial plate details.

I know compression is also not the best indicator for 2 strokes, but what's a min compression before it should be torn down?

Thanks.

Edit: 2011 intro and 2013 refresh? Not sure what changes...