My Ryobi planer couldn't keep it's dust collector / vacuum attachment shroud in place. Every time I hooked up the DC hose to it, the thing would start slowly sliding off.
What I did was to buy 1/2" longer set screws than what came with it, as well as appropriately sized fender washers, external start style lock washers and some SAE washers for the new set screws. Every screw was put in so that one of the lock washers contacted the plastic. Between the lock washer and the bolt head was placed a fender washer or a SAE washer (SAE if fender was too big).
I haven't used the DC hookup a lot since doing this, but have walked into the DC shroud quite a few times trying to "mountain goat" over to the new lathe. I figure my 300# frame smacking into the part is similar to hooking up the DC. Anyhow, the shroud is still firmly in place, so I'm sharing this tip in case others have the same issue.
Here are the pics:
As can be seen, I retained the original bottom handled screws and used fender washers over the external star lock washers (used to "bite" into the plastic shroud). On the top i bought slightly longer cap screws and used SAE washers with the external star lock washers.