If it was me I'd wear it. I wouldnt care about the other stuff, like if it was proper or not. Its your grandfather's, assuming he's passed on, its an excellent way to have a little bit of him with you on your wedding day.

The cleaning idea, is a good one though, and Matts recomendation of Danny Shearer would be the best way to go.

In the end though its ultimately your decision, whichever way you go, good luck with it and Congratulations on your upcoming marriage, All the best