Hey there , i got a Wira 1.5 just converted to manual transmission using F5M21 gearbox with clutch pump , im using Castrol MTF 80w90 GL-4 gearoil with it as far as i know from research this gearbox can't use GL-5 oil which will corrode & cause damage to the bronze syncromesh inside .

The issue I'm having is sometimes when shifting into 2nd gear kinda hard , can feel like 2 step movement when shifting & when shift into 3rd gear sometime can hear & feel a little bit of grinding but it will...