No one I know breaks the connections and drains the cooler at routine
oil changes...
if the oil is changed before it turns black then the oil cooler will
not have black sludge left in it.. The contained oil will be no
dirtier than what was drained and is diluted by the fresh oil...
Frequent oil changes is the solution...

Now, if you have a pan heater and you are coking your oil with so
called 'preheats' than that residue and char will collect where the
oil flow is the lowest, which is the cooler where the Vernatherm stops
the flow... The cure is to stop using the pan heater...

If you recently changed oil types to one that is more aggressively
detergent which acted as a solvent and loosened the gunk in the
cooler, then this is likely a one time issue... A self curing
situation...

GL .... denny