Why is the grease returning even after deep cleaning?

That thin, yellowish residue almost always points to a failure in the water temprature regulation or a blockage right at the inlet manifold. When water isn't hot enough, those fatty residues from plates and pots aren't breaking down properly during the wash cycle, and they just accumulate as a film instead of being scrubbed away. Since you've allready cleaned the filters and spray arms, the next step needs to be internal, focusing on how the water is being delivered. You need to check the heating element area itself. Even if the cycle is running, if the element has calcified or has a clogged flow path, the temperature will drop significantly once the dishwasher finishes its initial heating phase. That explains why the gunk seems to reappear within a couple of loads. If it's not reaching the boiling point or at least the neccessary high-heat range, the oils just set into the plastics and seals.

Another place this gunk loves to hide is around the main pump housing and the inlet valves, expecially if your local water is hard. Mineral buildup acts like glue, trapping grease and allowing it to seep out during the rinse and drying phases. You might need a more aggressive descaling agent than just vinegar to get into those hard-to-reach internal passages. Look for those rubber seals around the door and lower rack; they are designed to trap water, and they are notorious for trapping and releasing fatty residue over time. Fixing this internally is possable, but it requires pulling the inner wash tub away from the frame to get at the inlet valves and the pump assembly. If you aren't comfortable with that, a repair person can diagnose if the thermal sensor is giving a false reading or if the heating element needs replacement. Given the recurring nature of this specific issue, replacement of the entire internal heating unit is often the definitive solution.

I've seen this happen too, but maybe I'm focusing on the wrong thing since everyone is talking about the heating element. My dishwasher is a little older and I always use a super strong detergent. Do you guys think it might be something with the soap itself? Sometimes I read that using too much of that dish soap actually makes these fatty films worse because it doesn't rinse away right. I'm not sure if that makes sense.

I've had this same issue before, and it wasn't purely about the water temp, but the mineral gunk around the internal pathways. When I had to take one apart last time, I brought a small brass chisel. Just scraping out the hard scale buildup that was blocking the flow in the intake line made the biggest difference. It wasn't about raising the heat anymore, but ensuring the water could even move thru the system properly without clogging. It looked completley clear once the gunk was out.

I've seen this kind of issue crop up on older models that just lack a proper grease trap in the wash zone. It's not always the temperature, sometimes it's just the sheer physics of how the water drains through the rubber seals. If those seals are cracked or worn down, the thick, oily muck settles right in there and gets released onto the dishes during the final rinse. It’s a slow bleed, really. You might try treating those seals with some dedicated silicone cleaner, not just soap. It’s a simple bit of maintanence that often clears up those persistent streaks.