I managed to unscrew seized glow plugs on my 2006 Merc Sprinter (260000 miles). I first spreyed the glow plugs with the "blaster" when the engine was cold, then I used the van as usual for a week. Then I sprayed again when the engine was cold and I drove it for 30 minutes to warm it up . After that I sprayed again when it was hot and waited 10 minutes. Then unscrewed all 4 glow plugs with a torque wrench set on 14 nm.