Auto box advice needed

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My Dads 1993 320E 5 speed auto has some slight faults. When very cold the box seems to slip allowing higher revs than normal (not major but noticeable). In addition the 5th to 4th manual change does not work and the sport econ mode swich is goosed. According to the gbox specialist the swich assembly is 500 quid and will fix the latter problems but the slipping requires a box rebuid at 1650 plus vat. I am looking for a cheaper solution, any ideas?

NB the car is genuinely mint (old mans pride and joy 3k annual mileage allways garaged) with all extras working it would be a shame to get rid.