Thanks for all your responses!
A couple weeks ago, I sent out an SOS about my 300-F brakes locking up when the car was hot, with the brake pedal sitting high and hard, and the brake lights staying on.
This week I had my 2 1/2 year old master cylinder replaced, along with all the brake hoses. The old DOT3 brake fluid was flushed, and Castrol LMA (DOT4) fluid was added, on Jack Boyle's recommendation. There was some sediment in the old master, but the old replaced hoses looked good. Mechanic said the brake shoes and drums, wheel cylinders and springs all looked fine.
Testing it out, I went to a local cruise night Friday, and then a 90-mile round trip down to Morris, IL cruise night yesterday - no problems. Next test will be driving the F to Detroit this Friday.
Reporting on Morris, 823 cars yesterday, with only 2 finned Mopars in attendance - my F and Len Lulich's 300-E coupe.
Burr Ridge, IL