bvy: Just for the hell of it:

Take 100ml of fresh Flexicolor developer. Dilute it 14 times to make 1500ml working solution. Then add maybe 5 grams of sodium carbonate to the 1500ml. Then, at 90F, process C-41 film for 12 minutes in as much of this working solution as you need to develop one roll, using constant, gentle agitation.

You must might become satisfied with the results, and the temp is easier to maintain.

Now, Rollei-Base is not Flexicolor, but maybe the results will be the same as mine, I don't know. - David Lyga