I found the AAIB report into the engine failure, in case anyone is interested (I thought I'd do that before anyone else, me included, speculated any further!)
It's at
http://www.aaib.dtlr.gov.uk/bulletin/jun01/gwlac.htm
The report mentions the header tank which ST1 describes, and suggests that it may have been emptied during the period of the side-slip.
According to the report, no other similar problems have ever been reported in the PA18, and it was not possible to reproduce the problem afterwards.
Take care up there....
FFF
-----------