Centre cap rubber gasket - tuner wheels?

[ianrandom]

Hi, I have an 80's set of Remotec wheels for my SEC, they are the spoked effect type. The large centre cap covers the centre of the wheel and the bolt area, and its meant to have a rubber ring around the edge so it seats against the wheel nicely.

The problem is that mine are perished and I cant seem to find out where to get replacements. Is it just a case of using a generic O ring? they do look shaped but then they've been on there however many years!

Thanks in advance!