I have to agree with you -- all the grounds that were finger tight plus the air tank does point to someone in the shop either looking for a cheap rig for himself, or for a friend. The truck is less than 15 years old so it also would have value to a fire department, so it could have even been someone who knew an ambulance dealer who would buy it once it was 'fixed".
And none of what was "wrong" was major - everything could be fixed in minutes once you found it.
More and more -- not a conspiracy, but a fact.