The screw is a bleed port for the shock that is used when vacuum filling the shock during rebuilds. I would try to tighten it but don't over do it because it's only a 5mm bolt. There is an o-ring on the screw that seals it to the shock body, I would wipe the oil residue away and ride it. If anymore oil seeps from the area there is a problem. The other problem is if the oil was in fact pushed out then the nitrogen/air pressure will have been lowered and could cause cavitation if it dropped to much.