actually bbforks suggestion is in a bulletin i saw about model J regulators, they do recommend upgrading to the 'cobra' regulator.

The old Model J's that had the primer button were deemed a safety and fire hazard. They did make a change to them and took the primer button out but they still had plenty of issues with them.
Since then the 'cobra' regulator has came out and they released a bulletin to most parts suppliers and dealers to upgrade to the cobra.

I've also found rebuilding those things can cost more than just swapping one out. So now that's what i do, labor to swap one is ALOT less then the labor it takes to rebuild one.