Have had a 950SM, which is essentially the same thing mechanically, for 27000 glorious miles. They’re really reliable but there are a couple of things to watch out for:
Water pump oil seals die with alarming regularity, check for emulsion in the oil tank and lack of coolant in the expansion tank. Get a dealer to do the fix as its a real PITA (o/h didn’t appreciate the engine casing being baked in the oven for an hour either)
Magura clutch slaver cylinders are disgracefully under-engineered and get killed by heat from the engine. Some good after-market alternatives. Master cylinders are almost as cr@p. Take stupid fluid.
Carb-fed 950s (so not the 990 you’re looking at) have junk fuel pumps. Again loads of cheap after-market fixes, but if you stick to the 990 you’ll be ok.
There was talk of the generator control boxes being prone to heat death. Not had this on mine.
Brakes on the adventure are a bit underwhelming. Rear brake will squeal like an old leyland bus. This is normal. There is no real fix.
Other than that have you had a look on 950 Info?
I adore my 950sm, one of the best purchases I’ve ever made. Big friendly pussycat. Think I’ll go outside and give it a hug.