$500 is reasonable to fix an oil leak with an FTO motor, if that's all you are doing. Apparently it is a pain to get everything apart.
As a guide..........
Rik and Jo's serviced my car over 2 days before I returned to Tassie (100k service at 85k), replacing cams seals etc and I don't think I got much change from $1k when I supplied oils, plugs, air filter, oil filter, brake fluid, coolant etc etc.
My only problem was the new cam seals didn't seat properly, I also had leaks from front and rear crank seals and the rear rocker cover plus a few minor problems with clips in the top end, therefore I had to shell out another $1.6k (mostly labour) to get everything fixed (nearly every seal in the motor) in one hit by my workshop here in Hobart.
Haven't had any further problems...........except the unquenchable desire to spend money on performance modifications.
Cheers
Chris