Fin stack sensor and Kernal task - replace logic board?

Hello,

All the sudden my computer started running really slow. Activity Monitor shows “Kernal_task” using 300-1000% of CPU power and fans were running on high. Computer is effectively useless because it runs so slow. Took too the apple store and they said “Fin stack” sensor had failed their hardware tests and the entire logic board needed to be replaced for $500.

Resetting SMC and PRAM had no effect. They attempted 100% erase and install but it would take forever and never finish.

Can replacement be done for cheaper DIY? Is the “finstack” sensor on my model located on the logic board or motherboard or this that the same thing?