Got the same problem with my 1991 745T. There is a post in the FAQ about repairing the clamps. There is a link there to McMaster-Carr, an industrial supply company, where you can get new clamps to replace the broken ones. I just ordered 6 of them at $4.xx each. Don't remember the exact price, but it was cheap, well under $5 each.

The guy who posted in the FAQ used aluminum rivets (pop-rivets) to hold the new clamps on the bottom of the air box. Used alum. backing where necessary and glue of some kind to seal rivets.

Will give this a try, because it is cheap and easy. However, yesterday I took the air filter out to inspect everything and decided the design of the airbox in my Turbo car was stupid. Have to disconnect the AMM or MAF (whatever you call it) and the pipe from the turbo to the intercooler just to change the air cleaner. And, in the turbos, there is nothing in the big air box except foam to keep it quiet. So, I'm thinking why not fabricate a mount for the MAF (Mass Air Flow) sensor (which mounts to the top of the airbox in the turbo) and eliminate the whole box. Come off of the inlet side of the MAF sensor with aluminum tube (approx 2.5" dia) with a 90 deg bend. Put a K&N cone filter on the end of the tube and aim it down into the well where the box is. Voila! Easy to change, looks good, and easy to build an aluminum box around to keep hot engine air away from it. No need to fiddle with delicate MAF sensor to clean it either.

But will see how new clamps work first as they are much cheaper.

Oh, yeah, checked with Volvo dealer a few weeks ago, and a new lower airbox for my car is over $140. Suspect that non-turbos would be even more as they have more stuff in the box, like thermostat and valve(s), etc.

2nd edit: Until clamps arrive and I fix it, I have been putting a 3/4" thick little block of wood on top of airbox lid. This allows the hood to press down on the airbox lid and keep it shut. Also put some household insulating foam stripping in the groove in the box lid last night, to help it seal better on the filter. Did not use adhesive so it would be easy to remove when putting clamps in. Filter in there now is a Fram, and I don't think it fits right, does not fit in to grooves around perimeter of box or lid. Probably best to use genuine Volvo or, maybe K&N.