[DeTomaso] ZF Gear Lube Question

[B Hower]

I am getting close to putting engine and ZF back into # 3400. I dug up the left over lube from my last ZF oil change, which is Pennzoil Gearplus -- SAE 80W-90 GL5. It states on bottle--Formulated for Limited Slip Differentials. But recently (some where) I read that Lloyd B. had said to use GL4 not GL5. Do any of you see a problem with my past choice?
 
Thanks,
Bud #3400