envelop

When running large envelops (229 x 324) the staple rises after each envelop that is feed into the machine a smal amount, so after 40 envelops the staple wil be to low and the machine wil stop. The weird thing is that sometimes (maybe 1 out of 10 times) the staple rises after 2 or 3 envelops are...

Can anyone recommend a second hand Envelope printing machine? I am looking to buy a Second had Printinting machine that is good condition .