I've had good luck (knock on wood) with both Redline and Millers. Redline significantly smoothed out the shifting (a 336 box) in 693R when I did the renovation back in 07-09...I drained the 365 box in 3291R this past summer and filled with Millers from RD, and it seems to be working ok so far.
I don't see the advantage of GL5 over GL4 for our older technology boxes; it's like using the current oils off the shelf in our flat tappet motors; the 'advances' (mostly to satisfy the tree huggers who've forced all sorts of emissions gubbins into our drivetrains that react badly to the older formulations) removing anti-wear zn and K from the oils isn't necessarily the best (IMHO, and backed up by discussions with lube scientists I worked with at one of the major oil companies) for what we're running in our antique engines. FWIW, I run either VR-1 or Brad Penn racing 20w-50 (the old Kendall formulation, lots of ZN and K) in the power unit.
To bring it back around, I think you'd be fine with either the Redline MT-90 or Miller lubes. These transaxles aren't finely-tuned swiss watches...they will work fine with lubes that satisfy the standards which have been in place for decades and were current at the time they were pushed out the back door at Regie Renault (assuming this is for road use...track is out of my swim lane, so can't talk to that).
(But then again, I also supplement the engine oil with CamGuard (
https://aslcamguard.com/product/camguard-oil-additive-automotive-8oz-single-bottle/ no financial interest, etc., just satisfied with the product); I've used the aviation version since 03 and my Cessna engine seems to enjoy the treatment and the results when I tore the mill down to overhaul it bore out the published test results; the automotive product came out as a response to gear heads using the aviation formulation (which didn't hurt anything) in auto engines; the developer (who I know personally) just tweaked it to address occasional-use car motors...).)
