Removing the intake manifold is not difficult. It probably takes 20-30 minutes. Then you'd have access to the glow plugs. I agree there's a chance that one of the glow plugs could be stuck and break off in the head though it hasn't happened to me (yet). A major PITA if it does. I don't know about the harness. If it's just the insulation cracking, it can be patched up with electrical tape. No need to spend over a thousand replacing it.

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2004 VW Jetta TDI (manual)

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