I lost my oil filler cap, maybe it wasn't fixed properly when last serviced.

When searching for the part with my reg.no. I can only find the VW type cap which doesn't fit. Seems I need the older Favorite/Felicia type (already found one on ebay).

Is it normal that the information with suppliers can be so wrong?

The oil caps just push on and are held in with the rubber seal. If there were a significant amount of blow-by I suspect the oil cap would easily blow off. The 1.6 Felicia engine uses the VW style twist oil cap I think? Dealers probably just assumed all oil caps are the same - I am guessing this is the case with the VW oil caps.

If you want one for a Favorit/Felicia 1.3, if you can find a Fabia 1.4 mpi in a scrap yard, lift off the engine cover (2 10mm nuts hidden under a cover and a badge) and then pull. Underneath that is usually a spare oil cap held in the cover for a garage to put in while working on the engine. One of those will fit perfectly (I am not sure if they are available separately from the engine cover at a dealers or not).

Or find a Felicia in a scrapper and take the cap off that.

Or you could buy the right one from Jorily....

http://www.jorily.com/catalog/index.php?main_page=product_info&cPath=131_2_10&products_id=104