Reliability of O-300

Hello. Looking at buying another airplane (I tried cutting out the
middleman and just flushing $100 bills down the toilet, but it isn't
quite the same). I'm currently considering early-mid 60s Cessna 172s,
powered by the 145 HP Continental O-300, and would like to hear from
any owners of these planes and engines. I have heard and read some
very mixed and inconsistent perspectives on these planes. One guy at
our airport who owns a straitback 172 says he has never had to have a
cylinder replaced or top overhaul done in 20 years of ownershop, and
has made it to TBO three times with no problem. Another guy I know (A
mechanic who I trust and respect) has told me that if I buy one of
these planes, I should expect to replace a cylinder every third
annual, and that I'll almost certainly need a top overhaul in the 1000
to 1200 hour range.

I have flown in these birds before, and was impressed by the
smoothness of the engine, compared to the O-320. But if anyone has
experience with these engines, I would greatly appreciate any help
with the following questions, and any general advice:

1. What kind of fuel burn do you consistently get with an O-300? Is
the generally reported 105 KIAS @ 8 GPH true?

2. Does the autogas STC help reduce the problem with valve sticking?
If you have the STC, do you generally burn a mix?

3.In general, has your experience led you to expect to have to do a
top overhaul about halfway through the TBO period? What are the
ballpark costs of such an operation.

4. In your opinion, would it be worth it to pay the premium to buy an
new 172 equipped with the O-320E2D?

5. Besides the valve guide and cylinder problems (often attributed to
running on 100 LL), are there any other major problems that would make
this an undesireable aircraft?

Thanks for the help,

Cap