You can clean the rubber gasket all you like, and I've tried, but the OEM gorilla snot is almost impossible to remove and that's why you'll likely find a wee leak and it just pisses me off to have to go back in there to resolve the problem. It's just easier to spend $25 USD and stick a new one in there and be done with it.
I'm batting less than 50% on cleaning the old gasket and avoiding a leaky little leak.
Dave at present my 910R STOCK untouched valve cover gasket is leaking
can i fix it? yes, will i use a new gasket? no!
i will use Permatex RTV Silicone;
will it leak again NO, trust me, i've been doing this a long time
re; cleaning old gasket material.....
i use lacquer thinner or acetone, if they don't remove it, it can stay
my Aprilia RSVR valve cover gaskets started pouring oil at ~13k mi, both cylinders......at 30k mi the same gaskets are on there....glued on there with high temp silicone......they DO NOT leak
apparently MV got their cover gaskets from the same supplier as Aprilia they shrink on the exhaust side and leak
do the F4 covers leak? a lot of the time
are they flat? no.....is mine? yes, i flattened it with one of these;
its glued on too
my '67 T-100R didn't leak, i fixed that.....so why would i let my MVs leak?