Also I never could quite build up much confidence in a plane where the air conditioning NEVER worked

I had a VW beetle that by all reports had a heater that never worked. One of the best cars I ever had (until I let my kids drive it for a while).

As a comparison, I worked on another "brand name" (smaller than 737) airplane for which I received numerous "squawks" that appeared to have been already worked, but the pilots were still complaining. In more than a half dozen instances, I found that good engineers had delivered very good rework instructions in response to the same pilot complaint at least six times previous to my receipt of the same complaint. In every instance, the engineers had done a very good job of "fixing the problem" with the small difficulty that the part for which they fixed the problem wasn't the part currently used in the airplane. This maker had no "configuration control" and simply didn't know how to tell what parts were used in any specific airplane. They still don't, and I WILL NOT FLY IN A **** AIRPLANE.

(Don't ask which airplane, as I won't tell, but I will reveal that it was a UK design currently manufactured in the US, and that all of the engineers who had previously worked the problem were "green card Brits" working in the US, intimately familiar with the airplane - and I respect their engineering abilities, I just can't respect the airplane. Configuration management simply was not to Boeing (or FAA) requirements.)

With an airplane as old as many of the 737s, there is also the difficulty of maintenance, and it is common for major maintenance facilities to "punt" repairs not strictly in accord with factory specifications. I have seen numerous instances of "unauthorized" repairs by maintenance facilities, but on the whole, for Boeing airplanes of which I have knowledge, the major facilities have very good levels of competence, and I have no particular reservations about the quality of work done on Boeing airplanes by or for most regularly scheduled airlines. (In a not too distant past, I incorporated some of the "unauthorized repairs" done by JAL in the specification for a similar new Boeing part, although Boeing doesn't know that.)

There might be some questions appropriate to maintenance for "fringe" airlines, but I've seen quite a few of the recent FAA incident reports applicable to the 737, and am not significantly worried by anything reported.

Airline problems do need to be considered separately from airplane problems, since poor or incorrect maintenace can turn any fine machine into a bucket of bolts - or rivets.

John