These things are not really designed for internal component replacement and precisely due to problems you are having with yours, my company does not recommend replacement of any components of this system, but rather a complete drop in replacement controller.
You'll notice our warning here (which applies to the generic LL board - and any others that use the same type of system) :
http://spapartsnet.com/Circuit-Boards/5 ... 9_1_1.html
These headaches are just not worth it. The systems in place work fine for a number of years, but when they're done - they're done. Even in the field I never replace components of these systems. It's always a new control or I walk away.
Either of these two units will work for your system:
http://spapartsnet.com/Spa-Packs-Contro ... 8_3_1.html
or...
http://spapartsnet.com/Spa-Packs-Contro ... 8_2_1.html
Both of these units complete with a new topside control, cords, etc... ready to install. Plumbing should not be an issue as they both use the same size of heater.
Hope this helps.