Those short trips will do it, if you don't get it out for a longer drive on the weekend.

The engine cleaners can be harsh on engine internals, seals and so on. That is why BMW doesn't recommend using them. I would just do a couple of hot oil changes a week apart, and get it good and hot in between. Realize that the vent system isn't in an oil circulation circuit, so something you add to the sump doesn't necesarily get into the crankcase vent system.

How do you know that? Sludge is sludge. If it is already there, it better stay attached wherever it is. I personally dont want some solid pieces flowing in my oil and especially collecting at the oil pump pick-up strainer.