Sorry for needless post all.

Just got it apart. Plastic is stronger than I thought!

"Pull, pull ....... curse......... pop! "

FWIW, it was adhesive holding plastic parts of housing together at
centre near fan. I managed to carefully get screwdriver in there to
help it along, then pulled et voila!

Thanks!

--
Neil Nicholson. 1981 Air Cooled Westfalia.

http://web.mac.com/tubaneil