Advice Needed - AME Mess Up or..?

[tomcomet]

Hello. Looking for some advice from folks with way more experience than me.

The other day I took my new to me 1977 Skymaster (and the first aircraft I actually own) in for an oil change and a few small snags. My well respected AME suggested changing the spark plugs because more than half were below tolerances. Sure! Next I get an email stating that while changing the plugs the heli coil backed out with the plug on #5 rear and can not be put back in as the cylinder is stripped. Now the cylinder must be replaced and I am grounded for over a week when there is lovely fall flying weather AND I had a business trip scheduled. Ouch!!!

Thoughts? Opinions??