[Elecraft] KAT500: Does SN 12XX require LPF T/R Switch Rework Rev.E modification?

[Robert Felmey]

I'm looking to purchase a used KAT500 serial number 12XX and I read online
a few places about needing to upgrade the LPF board if Rev. D or earlier...
Is this correct and necessary?  Has anyone done this or had it done at
Elecraft? How expensive is it? Is it know what serial number u it's have
the older board?

LPF T/R Switch Rework Rev.E modification,
Elecraft parts kit: E850607

Thanks,

Rob
KC2VIC