£350 is a lot of money, considering the oil for an IO-360 costs about £40-£50 (Exxon Elite, the best), an oil filter costs £10, and the rest is a few hours' labour.
The "labour" is done mostly with the eye and a power screwdriver, and in a JAR145 company there is no need to have a torque limit on it so it's OK to chew off as many screw heads as you like. I have lost count of how many chewed up screws I have had to replace..... The really big joke is that when I was under a Transport CofA I was not allowed to replace them
