Firstly what are you wanting done by means of a service? A simple oil and filter change?
I service my vehicle myself. Doing an oil change is essentially like any other car, and actually one of the easiest to change oil on and the air filter etc as there is room to get to things in the engine bay......Spark plugs however are a nightmake, and if you have the V8 ( i assume by your name your's being the SS) then it is sometimes booked as a 3-4 hour job as the back passanger side plugs are a nigthmare to get to.
Hopefully someone will comment on the garages near you, dont be conned by people saying well its american so its specialist and will cost XXX more, its a car and simple to work on so should cost same (and only takes 5.2 l of oil). If you are confident enough do the service yourself
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'99 Z28 A4, 253 LS2 heads, 228R TSP cam, Patriol Dual Springs, Double roller timing chain, LS6 ported oil pump, OBX LTs, 3" True Duals, LS6 intake, 42lb/hr injectors, SLP lid + bellow, EFIlive COS 3 Speed Denisty Tune (self tuned), 3200 Circle D stall, CAI mod, KYB AGXs, Eibach Pro Front Springs, UMI panhard, LCA + Brackets, Strut Brace, Custom Subframe connectors, WS6 axle with 3.42s, 18" American Racing Rebels, US mirrors, 93 tail lights, 3.5 inch custom cowl hood. Mickey T's Street DRs on Vette-ZR1 wheels for the strip !
Best ET: 12.0 @ 116 mph (on a 0-60ft of 1.8 s)