Or you can seal them up with Polymorph (Polycaprolactone) - it's a plastic that is malleable at 60 degrees centigrade. A soldering iron may work, but you'll probably change the shape of the piston a lot. Stuffing it with Polymorph means you can make it a subtle and flat filling - I've been driving with 3-hole and 4-hole pistons modded like that for half a season in my DEX210 and my FWD Buggy and it works perfectly
