Planning to swap out my gear box oil at some point in the near future.

Haynes recommends EP 80W GL4 for the Favorit, and 75W/90 GL4 for the Felicia - although I believe the gear boxes for both are pretty much the same?

I was thinking of using Castrol Syntrax Universal part synthetic 75W/90 which mentions GL4 and GL5 on the bottle. Or maybe Comma SX75W-90 Semi-Synthetic Gear Oil - 5 Litres [CO-SX5L] - £25.99 - Wilco Direct - For All Your Motoring Needs Are these likely to be ok?

you just made me very afraid since my mechanic toped off the trans oil with 140 weight, i guess im gona have to do the same as you pretty soon to avoid damages