I was scrounging up info on the Tubefex motor pot, and found that the
manufacturer Alps makes two series of motor slide pots. The cheaper one, the N
series, is what is used in the Tubefex and is rated for 30,000 cycles. They also
make the more expensive K series which is rated for 300,000 cycles so it would
probably have a much longer service life. They unfortunately only come in the
100mm slide size, so it would have to be mounted differently. May be worth some
investigation/experimentation???