On a trip and had the oil pressure light flicker, decided to pull over and took it to a shop and they said it need to have the oil changed and there was sludge but they did a complete change and “top clean” and we were fine. Worked great for a couple of weeks after returning from trip but now oil pressure light flickers, on/off (so fast I didn’t know what it was at first). I’ve been watching for when it is idling, rpm’s or something else but can’t seem to see anything consistent. Any clues?