Hi Kev,
Can't say I've had this problem with my 93 900ss - I wonder if the the plastic windows have degraded in some way. No doubt it would have to be replaced with a full new unit but, they do come up on Ebay with some frequency.
As an aside have you checked your battery voltage and all the earth's recently?
Also, I wonder if the p*ss takers will be glad to pay for you to rebuild your engine when you can't see your oil press light come on
Cheers - Frank