Tire Sidewall problems of the 2008 BMW 335

Sidewall separation (right front) on bridgestone size 225/40r18 reo50a original equipment run flat tire at 20,000 miles. These tires seem prone to delamination. Very poor tread mileage for highway driving. Worn out now. Utqg rating seems exaggerated as I'm not in stop-and-go driving mode. These tires are priced $70+ to $90+ per tire more than non-rf tires and b'stone has a virtual monopoly. . . . BMW n. A. Only permits replacement of these tires and it really hits the pocket book. Contacted b'stone consumer relations and met a brick wall as they know they have you over a barrel. Wrote the pres. Of bridgestone and not even the courtesy of a response.