Volvo: Parasitic Load causing battery drain on Volvo S70, 1998 volvo s70, volvo s70

Question
I bought a 1998 volvo s70 2/3 months ago.It runs great but starting has been a problem after a couple of days. I assumed it was because I was only driving it back an forward to train station (1 mile)per day. Recently with bad weather its got worse. Checked interior lights all off - still got problem. I connected ammeter to battery and found current drain 0.3amps. Pulled each fuse out in turn - found glovebox/interior lights etc was the problem. I assumed problem must be related to door edge marker lights so I opened each door in turn. The current drain remained the same when I opened the rear passenger door so I removed the bulb. Success on current drain now almost zero!
Could the problem be the door microswitch - is there anything else I can do to confirm this?
I've read that microswitch is incorporated into door lock in s70.Can I clean it by spraying lock with WD40?
The interior light above the dash has been staying on as well forcing me to keep it switched off could this be of the problem with the lock microswitch?
If it is the lock can I fit a new lock myself?

Answer
Martin,
Those lock motors have been the fault of many problems. There have been at least two cars that I have replaced all four lock motors. That being the case, yes that switch could be your problem.
I do not think that WD40 would help, as a matter of fact it may even hurt by causing a  poor electrical connection.
You could disconnect the electrical connection from a suspected bad lock motor.