Walther MP5 red dot problem

[v2kai]

my MP5 Walther red dot recently lost its ability to adjust through the seven settings of dot intensity. I've tried a new battery and it seems all the intensities are now the lowest first setting. has anybody else had this problem? know any possible solutions?
looks like this:
http://img.villagephotos.com/p/2006-...P5Scopeweb.jpg

[ginnz]

the rheostat must be shot. see if you can take the cap off the adjustment knob and spray some electronics contact cleaner in it. it may fix the problem.