Just starting in this forum, so here is a greater explanation. I have a 5V Holton double bell that was purchased several years ago with the wrong valve pistons (my epic fail). I am hoping to manufacture pistons from silicone-graphite rod, but am concerned about getting the port holes right. Is there any resource from the engineering of the pistons "out there"? Would I be better off having a shop custom build the pistons? I suspect the cost of building 5 pistons might exceed the value of the repaired horn. Help and/or suggestions are most welcome.