So I have a negative experience with the SULEV warranty to share...
Car in question is a 2009 328i N51 with ~97k miles. I am the second owner of the car, and have owned it since 2016, bought with 32k miles.
At 40k miles it needed a valve cover and gasket. The cover was cracked. SULEV warranty covered it, but it was a fight to get them to cover it, my car sat at the BMW dealer for 2 weeks before they decided to cover it. In the following years I needed spark plugs and a coil failed, along with a OFHG. I did all that myself simply because the parts weren't that expensive, and much less of a pain to do myself instead of waiting for weeks for the local BMW dealer to "decide" if it was covered. They also conveniently never had any loaners available, which is fine, I mean I didn't buy the car from them so I get it.
Fast forward a few years to ~85k miles and the secondary air pump quits. Checked the wiring and tested the pump and sure enough the pump was dead. It's a fairly pricey part, so figured hey I have another vehicle to drive, it can sit at BMW while they figure it out, should be under SULEV warranty. Weeks go by again, more back and forth, and finally they replace the pump. I think that is the end of it until weeks later I go to replace a headlight bulb, and notice the hack job they did replacing the pump. The pump looked to be out of a different car. It was new, but looked like they did some wire splicing to make it fit along with using self tapping screws since the original studs holding the bracket sheared off.
And now the finale... 92k miles. I get a code for secondary air insufficient flow, but it's obvious the pump is working. I have a local indy shop take a look, and they suggest either the air valve is clogged/inoperable or the cylinder head ports are partially clogged. I replace the valve myself since it is an easy job/cheap part and the old one was pretty gunked up with carbon. Code went away for about a week then returned. Same indy shop told me it was likely the ports in the head being clogged with carbon, and I wouldn't be able to pass emissions (conveniently due this month) with that code. They gave me a quote to clean the ports in the head, which was reasonable, but advised me to go to BMW since it was a SULEV car.
I take it to the BMW dealer, and they have the car for a week before even calling me. They finally call and say it needs a new cylinder head. They don't send the head out for cleaning like the indy shop, they simply replace the entire cylinder head. They told me that it's likely BMW won't cover it, since I am the second owner of the car and would need detailed dealer service records for the entire life of the car. Keep in mind this car was dealer serviced by the PO, I change the oil every 5000 miles with BMW LL-01 oil, and have a stack of maintenance receipts, spreadsheets, and other dated documentation from doing my own meticulous work. In the end the dealer told me to pound sand and instead quoted me $16,000 for a replacement cylinder head.
I ended up going back to the indy which did the cleaning for a fraction of that and I trust their work more anyway.
The bottom line is I wouldn't rely on the SULEV warranty for anything, because it seems like any other manufacturer BMW will try its hardest to get out of covering anything significant, and in the long run the N52 is much cheaper to keep going and less complicated than the N51.