Welcome to the club, Allan (the dodgy rear brake club that is!).
Try this for a tip-top back brake
http://www.ukmonster.co.uk/monster/s...ad.php?t=58090
I did this on my 1100 Evo two-and-a-half years ago and the brake's remained firm throughout (I've recently replaced the fluid but no bleeding was necessary this time - just a flush through).