Top cover eh???? The side cover comes as separate part number, and no screws are included. also the screws that hold the cover on are the self tapping variety... So they are not captive, or whatever crap description you want to come up with.
You obviously have never seen a MS391. The three screws that hold the top cover on Are "Captive", and there are steel retainers pressed into the plastic cover, which is supposed to keep them from coming completely out. I went past the dealer today, and ordered 4 new screws...will keep a couple on hand for spares. Stihl has suggested that I install a small toothed washer under them, and even place some Blue Loctite on the threads. If you are talking about a "side" cover, you have obviously not understood what I am talking about. Plus, I have NEVER seen a "self tapping" screw on a Stihl chainsaw....or any other chainsaw, for that matter. You may want to "adjust" your meds.
Oh, BTW...I notice you are a "pewter" Stihl tech...is that one level up from "cardboard".