No foam inside of these M's, it's F's that have the foam that sometimes needs to be replaced. M's are the ones that you occasionally will have to bolt mod if too many of the plastic rivets come off.
I have brand new SEALED Lexmark Manufactured (circa 1995) M122's with Soarer's Converters for $65 shipped if you want something that will be future proof. Those have ZERO broken plastic rivets:
http://www.ebay.com/itm/271832202316Would be $65 shipped to the USA if you were to message me through here with your PayPal info with that same 10% discount.
Not trying to take over the thread here, just think it's a pretty good deal if you want something that will require no maintenance in the foreseeable future. These are actually the only older NIB model M's that I've seen that don't have broken rivets. Must have been using higher quality plastic or something.