Can another valve be used in place of the stv2 trigger valve? This thing is crazy expensive, $45-$65 and most of the other, which look dimensionally the same, are in the $8-$15 range. Yes there's the hole in the piston but maybe the piston could be switched into a less expensive valve. At the stv2 cost, and considering they break internally, after a couple of replacements I'd be better off throwing the stapler away and rebuying one that uses the TVA6 valves. Help please.