on the Putz's at least, they only seem to use them at non-swivelling junctions, the clamps between elbows are normal steel units. I am assuming this is to prevent exactly what you're speaking of.

Newer Putzs has them on the tip 90, and with the steel lined gaskets they put in there they don't last long since the steel gives the gasket alot less give, especially when it packs up with old mud, and forces the 90 to ride more on the clamp.

Dipstick: Could you Private Mail me the type of boom and Serial Number for your unit.You can either use the CP.com mail or my Putz e-mail woodsa@putzam.com

I have a really good pic of one I split a few months ago.