Redline ATF in E-34 (92 525it) HELP

[Logistic@xxxxxxx]

I recently purchased a 92 525it with 47,000 miles in 
excellent condition, or so I thought.  At 48,000 miles,
I converted all fluids to the following:
Rear diff  -   Redline 75-90 gear oil
Engine   -   Redline 10-30  (S. FLorida)
Tranny    -   Redline ATF  (Dextron II comp)
At 52,000 miles, I am getting an intermittent reverse gear.  Sometimes it
takes 1 min. to engage.  My local mechanic (independent) said it was bands
slipping and would require approx. $1200 to replace them.
1.  Should I drain the synthetic and replace it with the OEM BMW Dextron II?
2.  Should I have the oil drained and analyzed to see if the mechanic put the
     gear oil in the tranny and ATF in the differential?  

Any help with this is greatly appreciated.  I can't believe the tranny would
go after 50K.
THanks,
logistic@domain.elided

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