I have to agree, the werra's are beautifull cameras, I have 2 of them, I have a werra mat, fixed lens and built in exposure meter,and a werra 3, complete with the cardinar and flektagon lens, from a car boot sale, for the grand sum of 2.50p GBP, the seller wanted 5gbp for the outfit, but I found the shutter wasn't working and offered him the 2.50, went home and packed the camera and off to Newton and Ellis in Liverpool, a week later a lovely,mint working werra arrived back, cost me 60GPB for the shutter service, so for the grand sum of 62.50p I have a like new Werra 3 and lenses. I think you might have problems adapting a newer lens for the werra, I would stick to using the 2 lenses that you have, the Cardinar and flektagon lenses are lovely lenses.
Richard