Aha, the little strainer under the washer fill cap (which had somehow gone missing earlier this year) that allows ventilation was gone so I guess either excess pressure or vacuum in the tank was the cause because I popped the fill cap off and the washer pumps all work now. Ordered a new strainer thing (BMW p/n 61661365848)

Thought it was weird that the washer nozzles would occasionally get sad and cry... little drips of sad blooping out of them.

__________________