yeah, he runs it on ULP because he's an IMPORTER and he DOESN'T GIVE A CRAP about what happens to the cars, as they're not his for very long, lol..
as for your dad, well, he should be using PULP in his cars as well, as thats what BMW Recommend.
He could possibly be voiding his warranty (though, by the sounds of it, that ran out a while back, if its a 93 model), as BMW Recommend their customers use PULP