If the tape is weathered badly, best to replace it with Eternabond--do it right and you won't have to do it again.
I would think any baby/talcum powder would work on the seals. Think I have seen 'slide seal lube' in RV stores, but don't know if they do any good.
As to the power washer--many use them, others say don't; I have used one with the low-pressure/wide spray without damage. But it wouldn't be hard to rip the roof open with a jet...
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired