Starflex
The other big difference is the bigger end plates on the horizontal stab. The first couple of hundred E 's had a strake on the point of the nose and a surfboard on top of the dog house, supposedly as they had problems with the airflow over the horiz stab hence trim tab and end plates. I presume this slowed the machine down. many pilots claim the D is smoother, cant say I have noticed.
The D model has a higher vne of 156kts v 152. However I have owned 4 E models ( 2 with surfboards, 2 without), fastest was 135 kts at max continuous where as my D will do close to 145 at max cont. Mind you none of them like going that fast. Normally cruise at 130kts pulling about 72 psi in a D
Not sure they are any more reliable other than they were made by Hughes rather than MD. I suppose any company when it takes over another always looks to reduce costs. However I never noticed a difference.
Still one of the most fun machines to fly nearly 50 years after it was born, says alot for 1960's engineering