just found an interesting site here, where they specify which Penrite oil can be used instead of Pentosin etc.
Ever tried that? Might be cheaper
Example POWER STEERING FLUID
A little heavier than traditional power steering fluids. it is designed to provide enhanced wear protection and reduce noise in Australian conditions.
http://www.derek.com.au/penrite.HTML
I use Penrite in my engine and diff. I tried some of their gear oil in the gearbox but it didn't agree with it so I use Redline MTL in the box now.
But no complaints from the engine or diff.
Ken, from Melbourne AUS.
'89 535iA with a 5 speed swap.