I'd change the oil first. I run 15w-40 in mine. Maybe just enough difference. I'd check the voltage of the battery. As suggeted, just run it over to a parts store. The Fram filters for tihs car, if made in Turkey have a good reputation. I have used a NAPA filter too.
What brand of glow plugs were replaced with? Only Bosch or Beru. I had problems starting. I went through all the ohm meassurements. It showed no problems. I took out the glow plugs, and hooked them up to a battery charger. THe #1 cylinder plug was bad. After replacing it, it started a lot better. Also, might look into reaming out the carbon in the glow plug holes.
Tom