myself and dad have just rebuild the rear axle on the ardea pickup, this is basically a floorpan aprilia back axle , most of the componants are the same as or similar to irs aprilia parts around the diff however the front oil seal and bearing arn't, anyway ron francis loaned me a standard ardea rear axle to compare and its alot smaller than aprilia so i think the likely hood of them being the same seal is slim, all the seals we bought off the shelf and were standard metric, i think its probably easier if you remove the seal and get it matched then re assemble, i wouldnt rely on buying a seal on someones advice either because as i understand it there are 2 different rear axles on ardea's ( please dont qoute me as i'm no expert!!) so the seals may be different between them
, the only major factor in your favour is most seals and bearings in lancia's this age are fairly standard so hopefully you shouldn't have any trouble getting one, if you do get problems let me know and if i can help i'll phone my suplier for you, hope all goes well james