sticky shutter release: Mamiya RB67

First time running into this problem. Each time I release the shutter my button won’t naturally release. I have to wiggle to locking part for the trigger to pop back out. Does anyone know why this is happening?

It may be something simple as needing a touch of oil* on the button itself.
OR
grit or a build up of dust/dirt on the button or fitting it slides in.

* Try a VERY small drop of lighter fluid & that may be enough to help.

NO WD40 or other spray lube!