For the diffs yes

Transfer box I think prefers GL4 - something to do with GL5 being unkind to the brass bits in the transfer box
 
Can use GL4 or GL5 in diffs

If you google defender gl4 or gl5 you'll find multiple opinions on whetehr GL5 does or does not harm brass components

There is brass in transfer box, not in the diffs

I've always played safe and just used GL4, but others seem to have used GL5 with no ill effect
 

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