Removing speedometer glass?

Oi oi oi,

I've recently baught a GT and was suffering from the known 147-dash-rattle
(probably due to the colder weather). I found out it was the hard-plastic
of the dials, with the rubber of the dash itself, that caused it. I treated
it with a silicon based spray for keeping rubbers flexible. The good news
is: the rattle are gone, the bad news is ... well, some of the product ended
on the backside of the glass of the speedometer and left some stains.

My question ...
Is it easy to remove the glass so I can clean it? Or is it a hard job for a
clumsy guy and should I take it to the garage ? ;-)

TIA!

Frank