Kings Volvo in Westbury is where I source my parts now. Most of the guys used to work at MRG Volvo but, know the club members, their cars well, including these good old ones! Then things went pear shaped with new management and most setup at Kings Volvo.
Basic service items are straight forward and easy DIY jobs.
Fuel injectors - I used Jimathan (who I IIRC correct no longer does them). IIRC I may have had the set from my Volvo ME7 cleaned and fitted in prior to the remap. Any company that offers ultrasonic cleaning for injectors will clean the injectors out. Just make sure they fit good quality seals prior to refit.
Here's mine;
The TCV/BCS (turbo control valve/boost control solenoid) is the small box, that clips to the side of the air filter casing and has 3 ports coming from it which, the boost vac/lines connect to. These can become inefficient overtime with foreign gubbins and if left, will not only reduce performance and efficiency but, can in the worst cases impact boost, such as overboost in the wrong direction and cause expensive failures.
Other work is only carried out by either Kings Volvo (Westbury) or Tim Williams (Coalville).
There is a good youtube channel by an America guy, called Robert DIY who has some great DIY videos for working on these Volvo and well worth keeping to hand.