Delbourt

My experience here is with a Vauxhall 2L “red top” engine .
After re building the engine if fitted after market hydraulic tappets that came in a plastic box filled with a fluid of some sort.
Due to various delays some fluid was lost before installation.
One tappet was a right little problem and never did get better regardless of the number of oil changes and flushing agents used.
But changing the oil did quieten the rest down.
So, in conclusion what have you got to lose?
If it doesn’t work, put a flushing agent in and change the oil again, then “back to the drawing board”.
That would be my approach.