40 rolls in 1L of chemistry scares me. Changing development times on the SSK-4 is a hassle, plus what I shoot is too valuable to me (and sometimes can't be reshot) to risk sketchy extended-time development to save a few dollars worth of chemistry. Thus I use C-41 chemistry as one-shot except for bleach.
What's the density like at that point, after 40 rolls? How are the control strips if you run any?
I had an option to get a nice wing-lynch (version 5 I think) from where I work, but I passed. I don't do nearly enough processing to warrant the size and complexity of it, chemistry would likely go bad on me before I could use it all. The SSK-4 is the perfect size for my needs. If I was doing a lot of volume I could see a WL being viable. It looked well built and pretty well engineered.
That sucks if the Tetenal liquid kit is discontinued from B&H. That was a fairly decent deal, overall and gave good results in my experience.
Dilution/extending time is almost certainly going to give color crossover and weird unprintable results. Extending the time is viable up to a point, but not diluting, from what I have read.