I took an old sidecover that was totally stuffed, broke it into bits and into a jar with acetone, a day later it had melted into a treacle like goo.
On the reverse side of a cracked cover i made a shallow V and smeared the goop in.
Because its the same material it actually melts its way onto your side cover becoming a very zen like "one" with it.
I have not found it to break yet, even though the cover rubbers are hard as hell.
Hope it helps