I have a old Trek 930 Single Track which is about 15 yrs old. I have rebuilt the bottom bracket cassette several times. I now need to replace it. It is a Shimano BB-CS20-68x122.5 with a left side c.w. thread. All the Shamano BB cassettes I have seem on the internet are right side thread. Which model should I be looking for? I live in Northern India so there is no bike store just down the road. I have to order parts from Canada and wait for what I hope is the right part. Can anyone help me