I used some grease I had in my grease gun that I use to lubricate the moving parts on my boat trailer. a couple of squirts, and several openening and closings of the roof, and it now needs no assistance from me.
I would think that the lithium grease is what is recommended if I remember correctly from other postings.
The tracks may not be the problem you are having though. the sunroof cable could need lubricating. But it wouldn't hurt to grease the track first and see if it improves it.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.