I own a Citroen 2CV and I was interested in finding an oil filter available through the normal auto parts stores that would fit. By looking at the info at www.wixfilters.com and the info at www.wixeurope.com I was able to determine that WIX part #51352 was compatible and indeed does fit. I have also found that the same filter can be found at Napa stores rebranded as a Napa Gold filter part #1352, the filter itself is identical with the the only variance being the sticker on the box.
Below are some pictures comparing this filter and the OEM Purflux LS131 filter
Here are the pictures of both filters after 3,000 miles of use and the use of Mobil 1 15-50. While I am not an expert I feel that this filter is perfectly satisfactory for the 2CV.
The filter on the left is the Wix and the right is the Purflux
This is the Wix filter media
This is the Purflux media
These are what I believe is the Anti Drain Back Valve. The orange one is the Wix and it seemed much more substantial than the Purflux one.
For more information about these respective filters here are links from their manufacturers.
WIX
http://www.wixfilters.com/productinformation/index.html
http://www.wixfilters.com/filterlookup/PartDetail.asp?Part=51352
PURFLUX
This page is for informational purposes only. If it screws up your car it is not my problem.