Are they perfect, of course not.  But they are pretty good machines with good parts supply.  

Preventative maintenance can go a long way.  Drain the oil from each gearbox  individually, measure volume and see how it looks.  If its way low or full of metal shavings, fix it before it blows.

Using forklift with extensions makes it really easy to drop bar, first time we struggled with jacks and it wasn't very fun, just put the bar in mine last night and it took 30 minutes, could take it out now in 20 minutes I bet.

Maintain it like its a high speed precision machine, which is what it is, and it will work well.  Match blades on each module, if you need a new blade on one side only, replace both and keep other for good spare.  Sharpen blades with a grinder inbetween cuttings.  I have a 1431 with quite a few acres on it, takes some work but there are a lot of moving parts.

If looking at used, move each turtle (what holds the blades).  Turn very slow and see how long it takes for neighboring turtle to show movement.  If you only need to move less then 1/8" thats really good, 1/4" OK, beyond that it could use some work at some time.  Usually first couple modules inside of driveshafts will have the most wear as they have more power going through each one to drive inside modules.