Oil gauge flickers when engine reaches operating temp-low speed/stop/turns

What is your question?

Oil sending unit seems ok; I apply gas w/ brake to maintain a steady gauge at stops. I have added "no leak" to oil, and it helps for a while. I thought this May be vacuum problem with regulator valve on side of transmission ( an oil diaphragm inside), and have the part, but no tools/ equip to replace it. Before I send it to a shop, I would truly appreciate some insight as to whether this is advisable.