2015 Expedition left side running board won't function

I’m looking for assistance in diagnosis of my left side running board failure.
The condition has existed for several years on and off, depending on
weather conditions, road/dirt and lubrication. Today it attempts to close but
won’t any more. When the issue started and if I was on the outside I would
assist it by pulling up with my foot. This no longer works.

When either l/s door is closed the running board always attempts to close
but doesn’t. Not sure what the algorithm is for the running board trying again
when it doesn’t see it closed but when our speed lowers we hear it trying to
close again, repeatedly.
I’ve checked on line for possible repairs but nothing helps. On line there are
many examples for F-Series, Navigator and Expedition through many model
years.

My dilemma is the bracket through Ford is $533 and the bracket with motor
is $937. I don’t believe Ford sells the motor separately.
If I buy the bracket that may have too much resistance for the motor sensor
and it’s not the bracket, then I’ve wasted the 533 and then have to buy the
motor and bracket assy for 937. Obviously I don’t want to buy the motor
and bracket assy if it’s only the bracket.