Jim schrieb:

The factory did their "resistor" mod to no effect and I put a pair of
b2b switching diodes across input, but they still keep blowing.

Just take cheap "normal" diodes
Take two pairs "antiparallel" like this (fixed font!):

antenna line
(inner braid)
|
| |--|---|---| |
|-----------|---|---|--|-----||
| |-----1M-----| |
ground
(shielding)

and add an resistor 1Mohm (500k - 2M will work OK).

hth