What do you mean you "messed up" the power pin on the CPU?
The LET should just peel off. It can be a bit of a pain if it was thin in some places. The eraser will come off if it leaves stuff behind use a ball of eraser to "pull" the residue off this will work for bits of LET as well. Now you "can" put the board in a dishwasher but I wouldn't recommend that since you'll lose all the stickers and ASUS probably won't honour the RMA without them. As for the grease use a hairdryer and just clean as much as possible with a cloth any extra that comes out. After that I'd wipe it down with alcohol just to freshen it up a bit.