My question is, have ever heard of it making engine oil gel, or turn sludgy if you can call that a word? I haven't, but 05 Chevy Equinox I'm servicing had this happen. Not sure if it started before or after the use of sealer.
Usually sludge and gelling is caused by infrequent oil changes or no changes at all.
I have done a few motor jobs that had oil gelling and assumed it was the original oil that came in the engine.
I call most Oil additives "mechanic in a can", and most do more harm than good.
Regular oil changes prevent sludging and gelling.
One common cause of engine sludge is failure of, or lack of a PCV heater. Shown in the picture is the PCV crankcase breather hose. The hose attached to valve cover. Notice the small black tube below the breather hose, blue arrow, in a U shape. Notice also that it is attached to the breahter tube. This tube carries engine coolant. It purpose is to heat the incoming air before it gets into the crankcase.
Heating the incoming air is needed because it helps to evaporate water in the crankcase. Water that remains in the crankcase forms acids that then react with oil to form thick gel like deposits. These acids are the cause of sludging that is caused by excessively long oil change intervals.
Engines used for short trips are particularly prone to sludging because of the engine does not get hot enough to evaporate the water in the crankcase.