Club 80-90 Forums

Hi -not been on here for a while but hopefully some simple advice needed please.

Changing my gearbox oil - I've drained usual dark stinky oil out.
Opened new oil (Comma SX75w-90 GL4 semi-syth - researched on here to be correct) but this is practically clear!? (I mean clear like water)

Is this right or have I misread recommended oil specification?  And will it be ok mixing with old stuff still in the box?
(Previous research found 4.5lts +/- capacity but only about 3 litres will drain with box still on the motor.)

Nothings ever simple..  

Should be fine with this fresh oil

4.5 litres syncro 4 litres 2wd, fill to overflow is more than the fill level