The air conditioner vents on my '87 Westflia have suddenly started
spewing black foam - small chunks of some sort of semi-deteriorated
open-cell black rubbery stuff.  It looks like the remains of a filter of
some sort.

I've looked in the vents and the air inlet with a flashlight, and I don't
see any filter.  Similarly, my Bently manual doesn't show anything.
Anyone know what it is, and if there's any way to get to it short of
disasembling the whole A/C enclosure?  Or is it not really needed
anyway, and I should just wait for it to all blow away?