Hey, no argument here. If a TEL substitute added to autogas keeps the
Lyc (or Cont.) happy I'd use it. I'd just feel better knowing it was
approved by the federales aeronauticos... Interesting how avgas
formulation sounds more like an afterthought than a science.

When I said the margin for error is less than when driving, what I
meant was an engine failure on the highway means you coast to the
breakdown lane and call AAA on the cell. If the same situation happens
in a plane, you become a (heavy) glider pilot. The consequences of this
can be disastrous (obviously) if the failure happens during a critical
phase of flight or over water, mountains, etc. With that in mind, I'm
very careful about what goes in the tanks. The service manager of the
shop that annuals my Lance tells me about guys putting Mystery Oil in
the crankcase. It's not approved but these guys swear by it.