I've found the water levels are not adjusted for the custom cycles as they are for the programmed cycles. I too wash my vehicle microfibers in the Miele W4840, and before doing so I soak them in Biz, followed by washing them using Ecover Delicate Wash, in the Sanitize cycle with excellent results.

Because I bucket soak them, and even after wringing them a bit, they still retain water and Biz solution upon tossing them into the washer. There has not been a stain yet that I've not been able to remove. No fabric softener (but I'm sure you know this) and they come out soft; perfect for my next use.

Yeah. It depends how bad or not the batch is.

I might do a pre-soak with APC or some Citrus based stuff I have. Then it gets a quick drain/rinse in the laundry sink before I put it into the washer.

I do FEEL that MF branded cleaners may have a slight edge over a free-and-clear detergent. Besides, it's easy guesswork. 2 or 4 oz per load and then hand dry.

My issue with programmed cycles is the water heater. I like HOT washes and AFAIK, even with Hot on the programmed cycles, it uses the hot water and No Internal Heater...

It's somewhere buried here at GardenWeb, but I believe the heater kicks-in on the Hot and Sanitize, no matter what program is run on our model.