Bottom line: If the tubes are cracking, you've either got a problem with physical stress to the tubes or the chemical cleaning agent that you are using is eating them up / breaking down the plasticizers which keep the tubes flexible.
The physical stress part should be easy to verify and correct. As to whether the chemicals that you are using are eating up the tubes, i would try replacing the tubes and at the same time, try a different cleaning solution. What would scare me is that, if the tubes are getting eaten up, what is it doing to your vinyl ? While it is true that the tubes see a LOT more chemical solution than what any individual piece of vinyl would ever see, the initial and residual effects are probably not good to begin with. Sean
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