I had a TT running around 500bhp with auto box, had a HKS ALC 2 fitted to autobox ecu(simple job) then changed oil to Lucas Racing ATF (The best in my opinion) , never had a problem from there on , ran Santa Pod and track and blitzing all over the country to shows,meets etc, in my opinon frequent oil changes, yearly or every 5-7k miles, more if you use it like i did, also helps to get a sump plug fitted to auto box, saves having to remove pipes to oil cooler to let out fluids.(though of course you can not remove all the fluid in the box this way,but over a short period of time partial changes will eventualy give you that nice red colour!
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Tony