1. Synthetic engine oil is good for your engine, but... I there is a lot of sludge build up plugging up your seals, as the sludge is cleaned off you may discover some leaks. The biggest mistake most people make is to lower the viscosity with synthetic. Keep the new oil the same weight!
2. Change it when ever it gets dirty or at 200K when you get a new clutch!
3. The wires and sensors are not there in your model.
4. Because of knock sensors, you will not know when the timing is being retarded due to poor octane quality. Your best bet is to use 91 or 89 octane for a few tanks, recording your milage and then try a tank of 87. If the milage remains constant, then 87 will be OK.
5. Check at autoparts stores close to you. It is really the lenses, not the bulb, that is the real problem. I put Ecode lenses on my V70 and have been very happy.

Klaus
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1975 164 w/174,800mi (Sold) 1995 850T w/91,000mi, 1998 V70R w/129,000mi