It seems the major "counter" argument to this issue is that it's a cheap $20.00 part.
With an $8000 game there has to be enough profit left on the table to pay for your mistakes. Send out the customer a coin mech on YOUR dime. it's not their fault you didn't get your shit lined up before production. Offering to sell them the part (discounted or not), is kinda scummy. The black eye isn't worth it.
Think about it this way:
If people here bought a machine from a flipper, gave him the money, then was told the seller was keeping the coin mechs AND kept your money no matter what.......
.....we would see a rage storm of threads about being "Choggarded".
Think about this while you're at it:
Those HAPP coin mechs linked above are much closer to $30 after shipping and sales tax (then they are to $20). 1500 omitted parts is $90K. Not to mention the money saved in not configuring them for each country during installation. What's the real amount that you're saving the manufacturer?
.....hey, I'm sure he's ok with you giving him a bonus after paying a premium for the game. I wonder how long before mechs are optional on new Stern games. With this kind of money being left uncontested by the customers, you know they've noticed.