For the sake of an extra £18 (if you're 8v), you could just buy a full set of new tappets, save the cost of faffing about (I should know!).
Try rebuilding your current ones first, its free and doesn't take long.
I don't much believe in oil additives, but a mechy mate of mine swore by Lucas Oil Stabilizer when his motor was tapping and burning a little oil.
For the record I did an ATF flush and although it didn't much help my current tappets, it thoroughly cleaned the inside of the engine, my oil is still golden now
