rubber

Hi, I have a 1996 Seadoo GTX Rotax, There is two black covers just behind the spark plugs with a little red circle on top(I have attached photo), 1 is in real good condition(right one) and the other the rubber inside is broken(left one), Can I just leave it off? and if I need it on, what are...

Anyone have any suggestions on what to replace the rubber(ish) handlebar cover with on a Seadoo SPX. I don't much care about the color. Is anyone making anything aftermarket out of a different material?