7AFE Transmission a bit notchy... Options

[englishdas]

The more I drive the car, i.e over 10minutes, the notchier it gets slotting back down from 3rd to 2nd or 1st. It's not terrible, but it's not right.

I reckon the condition of the Trans oil is my first stop, and have tracked down a supplier of MT90 'EBAY REDLINE MT90'

Now, I know that the capacity of the Trans is 2.6L (thanks, Rusty for C52 Trans Thread) So do I need 3 Bottles of this stuff, and (obviously not over-)fill it purely with MT90, or do I measure out standard 75w90 gear oil at about £7 per litre, and add the full bottle of MT90 to make up the 2.6L?

Am I making sense and/or overcomplicating it?

[VavAlephVav]

people say that MT90 works the best, IDK if there is any benefit in mixing it especially since most gear oil is GL-5, the GL-4 stuff is supposed to work better for the synchronizer.
I have seen a number of articles that say if you overfill it will drag a bit. 2.7 or 2.6 is good to shoot for but it should not be dripping out the fill hole, if the car is level you might
be able to stick your finger in to the first knuckle and feel the oil level. better to measure it.