I bought a used 18 850 154× 3" and it's been flawless. I out 830 miles on for a total of 1385 miles.
Favorite sled ever, ery fun, quick, and so far no issues. No problems with engine, runs strong (but I do worry about it), Hps can at about 900 miles, belt life has been good. 2nd belt but it was replaced on warranty due to a clutch tower bolt breaking and getting caught up in clutches. Ski doo replaced all clutch sheaves.(.recall bolt), in all fairness, I should have got it in for the update.
Clutch temp is what I conside normal, stock clutching and gearing and I think it works great.
Track is in great condition , and a couple times early in season I was sure I was going cause some damage spinning out on stumps and rocks.
I've been super suprised by the strength of the front end. I've bounced off of and had direct hit's to the front A arms, and again thought something would at least be bent but it still looks great.
Smucked a few rocks this year and no a arm or bulkhead damage.
Again, I am hoping what a see on the internet about the motors is what I've seen for the last decade about doos various issues, esp clutching and gearing , and the sleds I've had have always been great, ran stock clutch, and no issues. Hope this 850 is at least a 3500 mile engine.
I do think for the price you pay they should be a 5000 mile engine.
Now....knock on wood.