Thanks for the reply. I'll look into the coolant fitting to the block.

I actually just had my fuel filters replaced two weeks ago in conjunction with the replacement of my fuel pre-heater, which was leaking. My shop (Mitch Carr's) had thought that should fix the loss of power, and it did, for a time, but now it's back.

My pre-filter currently looks sparkling clean so I'm certain they do not need replacing again.