During this year's condition inspection, I found cracks in my heat muff end-caps...again!
So instead of spending another $40 to replace them for the fifth year in a row, I purchased a TurboHeat muff from Dave Edwards (through Aircraft Spruce). Could not be happier! Better heat, easier installation, more compact for my tightly-cowled IO-390, and outstanding customer service for my odd layout (inflow and outflow are offset 120 degrees). Highly recommended. Wish I had done this years ago.