Hey I know this was a long time ago. But bwrgtr did the 30mm one fit well? Also how thick was it? I found another one on rhdjapan moonface brand which is a different product code OWC030 which is 30mm for a glass thickness of around 3-4mm. Here's the link for other ppl who are looking for this currently
http://www.rhdjapan.com/moonface-racing-rear-wiper-hole-cap-30.html
Also would I need a plug for the wiper motor?