I'm starting to get a sense of what a bad idea it would be to add the passenger air bag. I wasn't even thinking of the "L" word (liability). I actually was thinking of doing it myself, taking parts from a later 126 with the passenger air bag. Now that I think about it, doing that myself makes things even worse.
Like many people in this forum, I'm an avid DIYer. I've been upgrading the interior of my car to make it look like the '89 + facelift, including adding the adjustable rear seat. For me, in addition to any perceived safety benefit from the passenger air bag, it also had the "kewl" factor. However, there is a big difference between truly cosmetic upgrades, like new door panels, and safety related things, like an airbag. No one will be injured if the door panel malfunctions ... Like the song says, "You've got to know when to hold 'em, know when to fold 'em." I'm folding on the passenger air bag.