Sticky rev counter on 1150 GS

[Eendstop]

The rev counter on swambo's bike has some dust on the inside of the glass on the revcounter, which was not a prob for a long time, but lately, sometimes the rev counter would stick at a spot, say 3000 rpm, and needs some tapping to function normally again. More dust must have come in I assume.

I can do many technical things, but have never opened a rev counter.

Any do's and don'ts here, oh knowledgeable ones?

 

[Welsh]