Hi
I put a Oetinger 85 deg thermostat (instead of 87) in my WBX some time ago. I felt it was time to replace it but couldn't buy one again so I modified a Mercedes one. You can get them in 75, 80, 85 & 87 degress celcius. The only mod needed is to reduce the diameter of the lower shut off flange to the same as a the WBX one. It takes few minutes on a bench grinder to do this.
Regards Steve C