My 1986 190e, 130,000 miles recently flew through it's MOT(unlike last year) The garage, almost in a fit of pique, advised that the auto box needed a strip & rebuild @£1300. Only fault I was aware of was a clonk when going from D to R when stationary and hot.(The box not me) When cold all OK. Prop & Drive shafts OK. Is there any idiot's guide that is available to check my box?. or must I go to our local MB dealer for a check out?