After my 300 TDI wouldn't stay timed I opened up the case and stared at it for a long time. After a while I realized the crankshaft timing gear wasn't quite aligned with the outer woodruff key cutout. After pretty much destroying my gear puller and 8 M5 bolts I was able to get it off. Make sure you use a hammer and chisel to knock it back in line before going after it with a puller. I replaced it with what I think is a higher quality gear and put the crank pulley bolt on good and tight. Now she is right as rain.