You must clean the rails first with an acid brush and carb cleaner or something to get the caked former lube off. Clean it real good, then apply only MB sunroof grease.
I had to crank on the emergency mechanism with a ratchet to break the sunroof open when I first got the car.

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)