Just for information:

I had run flats on my Z4. Picked up a screw in my left rear on my last trip
and the sensor went off with me still 60 miles from home. I pulled into a
gas station a filled the tire up and reset the sensor. Made it home with no
problems. Next morning there was zero pressure in the tire. I filled it up
again and drove the 4 miles to the tire dealer. That's the good news.
Everything worked as designed.

There is 15k on the tires and the rear ones showed a fair amount of wear. I
had the option of buying two new RF for the rear for $260 each or non-RFs
for $184. I probably had another 5k on the front tires (I managed to get
40k on my Mini-S run flats which amazed the dealer).

The dealer said they don't repair RF tires so if I have another flat with RF
I would have to buy another tire. Also I could not mix non-RF on the rear
while still having RF on the front because it would severely affect the
handling. He mentioned it is recommended that if a vehicle having full time
AWD has a flat with RF and there is less than 20% tread left on the tires,
they recommend replacing all 4 tires. That makes sense when you think about
it.

I replaced all 4 with non-RF tires that have a mileage guarantee of 45k
miles (no mileage guarantee on the RF). I figure I can get them repaired if
there is a slow leak (which has happened in the past with my truck). If I
get a flat on road I will have AAA tow me back to the station and have the
tire repaired. The dealer I bought the tires from will reimburse me for the
repair or do it for free if I do it at one of their stores. I decided not
to get the BMW mobility kit because I have read the compressor may have
difficulty in pressurizing the tire if it is flat and it is difficult to
repair a non-RF tire when "goop" is sprayed inside.