My 99 slk230 is cutting out it doesnt matter if the engine is hot or cold and when it cuts out the cooling fan comes on. I try to restart but the engine doesnt turn over. Eventually ot starts and runs perfect until the next time. I know other slk owners have had the same problem and it seems that it may be the crankshaft position sensor. Firstly where is it, what does it look like and is it easy to replace. Can anyone help.