While I haven't had many issues on a Stern NIB machine, I have had a few with CGC.
#1: In my MMR, the Castle tower had a bit of the plastic flashing that needed to be trimmed, as the ball got hung up in there about 30% of the time. I put in a ticket and trimmed the plastic and the ball stopped being hung up. I told them in my ticket that I trimmed the part and it now worked fine. The next day after putting in the ticket, Doug Duba started the process to get me a new part. It came a few days later.
#2: My AFMr was damaged during shipment, I refused delivery and call my Distributor. In a few weeks I had a new machine coming off a truck.
#3: While not as bad some people experienced, I did have an issue with my decal on my Monster Bash. I never did submit a ticket at CGC.
The left edge of my side art was peeling back, about 1-inch below the lock down bar.
I had posted here on Pinside (post #1520 on Monster Bash Remake (MBr) Owners Club) to see if anyone else had an issue.
I was contacted via PM by Doug Duba to which I PM'd him back. He apparently reads Pinside.
A few hours later (on a Saturday late afternoon California time) Doug called me at home to discuss the issue. I explained and told him I had pushed the side art back down with the blunt edge of a razor blade and would let him know how that worked out. I also put on flipper button "half-moon" shaped plastic protectors. The protectors kept any hands from rubbing that area directly when playing a game.
Had several people play the game over that Christmas and the decal stayed stuck. So I emailed Doug that I considered the issue solved and that I required no further assistance. He thanked me in an email reply.
So I can say that in my experience, CGC's customer service is great!
So, good after sale service can be done by a pinball manufacturer...and CGC seems to be that manufacturer (for me).