Unless a side-cover is significantly warped/dented and/or the screw/bolt holes have been distorted inwards (you can punch them flat), I have never had a leaky side-cover after putting gasket-sealer on the side-cover&gasket and then using no sealer between the gasket&block(/head). If everything is flat, and you do not over-tighten the screws/bolts, you should be leak-free.
Tim
