I'm far from au fait with all the technicalities :), but I did think the existing battery going completely flat may have knackered it, so I put a brand new one in.
At the moment I'm pulling #1 fuse while the car's stationary, and the voltage is still holding steady around 12.7V...
Yes, that's basically what I did to find the source of the drain although I always disconnect the negative to avoid the possibiilty of a short to the body.
The parasitic draw is 40mA across fuse #1.
Having been away for a couple of weeks, I came home and went to start Occie, my Series 2 3500S, only to find the battery was completely dead. No voltage reading at all on the multimeter.
Managed, to my surprise, to get it back to seemingly fully charged using the CTEK charger in Recondition...
Richard's advice is good, but I've always gone for Castrol SMX.
But.....it's funny how progress never seems that way.......now rebadged as this mouthful....
Castrol Syntrans Multivehicle 75W-90 Car Gearbox Oil
Maybe it depends on the wheel diameter......
A titchy Halfords special might certainly struggle, but a beefy 3-tonner from a reputable company works just fine. Maybe that's why I have no problems at all on 60mm blocks.