I drilled a new hole in the cover for mine. Currently, it is replaced by a magnet which I felt added more value. At some point, I will redo my cover to accommodate things better.
For sure U need a vent.
No vent can cause collapse of lines and even cave in the tank walls but usually the engine stutters and stops B4 any damage is done.
For that matter an engine that is starving for fuel is actually running VERY lean which is the recipe for burnt valves.
How often do you clean your magnets these days? Are you still getting a lot of debris? I put a couple on my oil filters, but I have always thought your solution was far superior.
On the subject of oil quality, I did notice that running my PT driving a wood chipper for two hours really improved the response rate of hydroback, almost as if there were dissolved gasses or water in the hydraulic fluid.