Cleaning the inside of a MCRES is a pain - I had to remove flux from mine (I was too lazy to rinse properly).

Here's what I did (and it worked a treat):

http://www.xtremesystems.org/forums/...58&postcount=4

(if you don't have "Bounty" (now called "Plenty") then use any kitchen towel that is labelled as "strong when wet" - i.e. the stuff that won't fall apart in water)

HTH
J