The oil for gear, transferbox, diffs, swivels is EP90 GL4. I've heard that EP90 GL5 is not good news for series gearboxes etc, but motorfactors tells me that GL5 supercedes GL4 and will do no harm.

I've used GL5 in overdrive, also rear diff.

Trouble??

The API GL5 is the lubrication specification, not a list of what is in it; altho' GL5 has more Extreme Pressure additives than GL4. However, it is a bit more complex than just 'GL5 will eat your gearbox'

Some GL5 spec gear oils which won't eat bronze (or other copper based bushes) but then there are ones which will.There are no GL4 spec oils which will affect phosphor bronze.

You need to find an EP90 of API GL4 or API GL5 without "synchros corrosion risk".

What you have look for in the spec list is "API MT1"; this is a test for sensitivity towards copper.

Thanks for the explanation Andy. I'll check spec on EP5 but i don't recall any mention of API MT1. I'll replace oil ASAP with GL4. I wonder if draining the GL5 out is enough or will traces of it remain in the overdrive? Should I flush it out with petrol or so do you think??