Too bad my Dad won't sell his, he's right up the street from you in Uxbridge!
We looked around quite a bit and I found him a JD 310C in very nice shape. Can't even remember the hours, but well under 4000. It's been a great machine, but as his age advances the use of the machine declines.....he's lucky to put 50 hours a year on it now!
I've always liked CAT and JD hoes, Case probably the most popular, but as I recall they weren't made as beefy as the CAT/JD. Lots of CASE machines would have welds on buckets/booms, etc. Now this was many years ago, only opinion only on what we saw, just a small inkling of the market.
I was recently shopping for an excavator, and looked at a Kobelco 160....very nice machine, Cummins motor just purred....pins/bushings/undercarriage tight/nice. BUT, it had 9500+ hours.....as others have said, it could last a lifetime, or it could last a few weeks. The bigger the equipment, the bigger the repair bill....so I walked away. Ended up with a Cat 312 w/4800 hours, absolutely love it.
I would advise you get as smart as you can about the equipment you're looking for, and consider a local equipment dealer's mechanic check out a piece of equipment you're seriously interested in. Follow him around and ask questions, learn all you can quickly! I did this with the first excavator I looked at, very glad I did cause the seller was trying to snow me. Cost under $200, money well spent.
Good luck!