Link is below:
https://www.ebay.com/itm/401789956792
The seller also lists another 188L diff advertised for the 1 series:
https://www.ebay.com/itm/153446641798
The listings are identical as far as I can tell.
The different gear ratios are a superb explanation. I had never considered that. Or rather, I guess I had assumed that the spacing (between ring gear landing and pinion center-line) would be identical so switching between parts would be more convenient. This way, the thickness of the ring gear would be different depending on the pinion pitch diameter.
P.S. mad_hatter, I am classed in STX as well down in Texas. Let me know if you'll be at SCCA Nationals in Nebraska this September. I will be there (not driving the 1er).