I've never felt the need to use the stuff in forty years of motoring, just regular oil changes. I do accept there may be a need in exceptional circumstances, but I've not come across any.

Generally, just an excuse for the garage to extract more cash!

Have a read of my posts here:

www.honestjohn.co.uk/forum/post/index.htm?t=83817&...6

and here:

www.honestjohn.co.uk/forum/post/index.htm?t=104173

We just bought the wife a C1, 2 1/2 years old with just 6k on the clock. The oil on the dipstick was beautiful and clean. But there was mayo in the filler cap. This persisted even after 3 weeks of commuting 14 miles each way. So I flushed it using Wynns Engine Flush for Diesel. I then removed the cam cover. The flush had done the trick getting rid of the mayo, but the surfaces around the cams were showing signs of starting to varnish and sludge up. I cleaned the cam area mechanically, then after reassembly flushed the engine with Comma Flush Out. The Oil on th edipstick is now so clean it is almost impossible to see after 500 miles. And the wife reports the car is running much better (this from the woman who drove 15 miles home from work on a flat and reported the car "makes a strange noise"). We're also now getting 400 miles a tank vs 360 miles when we first bought it.

Just the opinions of one dinosaur.