I wouldn't put anything on them really, maybe the smallest amount of oil to help it thread just right.

I will say this, if you found several screws "not even hand tight", someone was probably not paying attention when they were replacing the last set of seals.

I would do it by spec for tightening it up, then check it next oil change. I'm sure it will be good to go if you have a new valve cover gasket on it.

Also, make sure the nuts on the top of the cover are tight, as that will let oil in several tubes at a time if they are loose.

If you tighten them right, they should stay that way.

 

I think the valve cover nuts are only supposed to be torqued to something like 7 ftbs. If you don't have a small torque wrench, I would suggest using either a 1/4" drive ratchet, or socket screw driver to tighten so you are less likely to put too much force on them. Turn them down evenly, a little at a time. Good luck