http://www.club202.com/forums/showthread.php?s=&threadid=3109&highlight=wiper
I've done this on my c280 a couple of times over the years. It's dirt simple. Use lithium grease only. The old grease will collect in a hardened blob at the end of travel on the slides. Clean it off. I have found the lithium grease good for a very wide temperature range. WD40 has poor lubricating properties, and if you are going to go to the trouble of removing the transmission cover, you are as far ahead to use the right product.