I'm not familiar with the 601's but why are you afraid of pulling out the intake manifold? I've heard of people changing glow plugs without taking off the intake manifold on a 603 engine, and I think they're crazy. I always prefer to take the extra time to get the proper access that I need to do the job properly and comfortably rather than trying to save time by twisting my bones and scraping my flesh which may actually make the job take longer to complete.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL