My 02 745 is losing coolant (again). It needs a top-up about every 1000 miles. I've had several head gasket repairs and the crossover pipe done. Literally thousands spent out of warranty in addition to warranty works done. The car has 100k miles and is otherwise magnificent but Im reaching a point where Im considering adding a coolant system sealing product. Even after the last head gasket repair I was topping up monthly.

I often get a yellow engine light briefly on cold startup. I believe this is a little coolant boiling out of one of the cylinders. Usually clears within about 30 seconds.

I hear both positive and negative feedback on sealing products. Im worried about clogging up the heater matrix or the radiator itself. Ordinarily I'd just get the repair done but my experience so far is that repairing coolant problems is difficult, expensive and very unreliable.

Should I just keep topping up until it gets serious or would a chemical solution prevent things getting worse quickly?