just sayin Hanso ,I use Dana Spicer premium synthetic grease P/N SPL1051 on all my uni joints and slip joints on the centre bearing slides ,it's made for use in Spicer 44,000Lb truck bogie drive units so far
it has worked without drying out on the big C109 Suzuki splines and on the rocket as well , my reasoning is if it works on the big truck drivelines the teeny weeny splines on the bikes should be OK, the tolerances on the Spicer units are just as fine as the bike splines, readily available in OZ I am sure someone will not agree but it works for me
you can buy it at most Truck Parts supplies outlets (no Ebay orders)