When I brought the 850R home from sitting for 9yrs in a farm shed I rebiult the following:
All seals, crank & cam, pcv
Genuine volvo water pump timing belt, serpentine belt kits
Geniune volvo engine & sub frame mounts.
Vacuum hoses, plugs & filters
Also but not necessary : auto oil cooler, peirsberg TCV.
The end result was worth every cent, motor sounds so smooth, Dosnt use oil and performs brilliantly.
Basically I believe if you want the engine to look after you and be reliable you need to look after it and create your own service history.