I own a 166 '98 2.5L car and from that i've gathered.
Besides the obvious in all cars (oil changes and such)
A) I would check timebelt changes, depends who you ask but changes every 50-60.000km are recommended.
B) Check front Wishbones or all wheels for that matter. It's a heavy car on the front and wishbones go bad quickly. Need to replace one :/
C) Check top Engine mount (can be found ontop of the engine on the left. Rubber in the mount seems to go early in the cars life, just replaced mine.
D) Aircon, check if the aircon and fan motor are ok (i've had my motor replaced.
I think that about sums it up mind you when i bought mine i didn't notice the B, C and D needed replacing, but fortunatly it wasn't very expensive.
GL M8 and you'll love the car if it threats you right
