[Leica] Elmar grease worries

[reviews_ed.hifichoice@dennis.co.uk (Alan Sircom)]

I read somewhere on the net about a problem that besets 'thin' 90mm
Tele-Elmarit lenses. The suggestion was that the animal-based grease
can affect the rear element of the lens and effectively destroying an
otherwise fine lens. I have a late-model Leitz Canada version of this
lens which is in tip-top condition and used regularly. I would hate to
wake up one day to find this important lens in my arsenal rendered
useless, but would prefer not to have to take the time and expense of
having this lens re-greased for no real reason.

Is this grease problem an urban myth, or does anyone have positive
proof of it aflicting lenses? Please no "my best friend's golf buddy
once knew this photographer" stories. Thanks.