That sounds like the second type of stuff I described - note it says 'does not harden' and doesnt say 'silicone rubber'.
For a sidecover etc, it's best used as a gasket dressing, not a gasket replacement, as it only works best when it ends up as a very thin film - whereas a gasket is designed to take up some surface irregularities - and so is silicone rubber instant gasket.
As I said before, if you've never used gasket compund before, keep it simple and use silicone rubber.
(I know it didnt cost much, but if you decide to get something else, I'lll buy it off you, as I know you need all your dosh
Oh, shout if you need a translation of anything btw