Who said I didn't? But you still refuse to acknowledge the point that
an oil leak could develop that you or your mechanic DO NOT KNOW ABOUT
and you are taking a risk. And as you said, Rapco (and others) already
know how to fix the problem.

With enough money, MANY (but not all) problems can be solved. The
amount of money needed may exceed the utility gained by doing so This
is going to get a little long-winded, so bear with me.

Dry vacuum pumps are mounted either vertically, as in the O-200, or
horizontally, as in most every other engine generally encountered. The
oil that gums up the vanes and causes them to snap probably leaks from
the accessory case shaft. If the vacuum pump is mounted vertically,
you've got a problem - seals drip, even good ones, so oil WILL migrate
towards your pump shaft, maybe a little, maybe a lot, but it happens
ALL THE TIME. But the key to a solution lies within the problem itself
- you have a RELIABLE source of oil to keep the seal on the vacuum pump
happy. Your goal is to essentially regulate the amount of oil that
gets INTO the vacuum pump to a slight sheen on the input shaft and no
more. Between the flinger and the seal, you can do that. (Even so,
I'll bet the life of vacuum pump on a C-150 is, on average, less than
that on a C-172 - those of you with maintenance experience in training
fleets can shout me down on this if you know better)

Mount the accessory drive and the vacuuum pump horizontally, and you no
longer have access to this solution. You no longer have a reliable,
everyday source of oil to lubricate the seal that "abripl" thinks
should be there on the input shaft of the pump (some oil may creep
along the shaft, but gravity is taking most of it down toward the
ramp). If you put one there anyway, it would burn up in a few hours
running dry on the steel shaft, and wouldn't be there when you REALLY
needed it, for the non-standard rate of leakage out of the accesssory
case or wherever.

There are seals that will run dry. Some exotic elastomers claim they
can, as lip or face seals, but life is short even then. A labyrinth
seal, as used in steam turbines, might do it, but they require
exquisite precision not just in the seals themselves, but also in the
bearings that support the shaft.

The engineers at Rapco, and Edo designed their pumps for the
application at hand with a compromise between cost and risk, and given
that Nature Abhors a Vacuum, it's a friggin' marvel they work as well
as they do, as long as they do, for as cheap as they are.