Check if it's not your RAM that is degrading.
By far DDR2 is the most sensitive component in any Intel combo.
If your temperatures and volts are ok, I believe the mobo is alright.

But you have to see that 575MHz FSB is not a normal thing you see everyday
Is that 24/7?

Some A64 were sensitive too. With time the OC degraded. I don't know about Core 2 Duos.