Once you have it split and all the little balls and springs are lying around, use carb or brake cleaner on everything and shoot copious amounts into the valve body cavities and cylinders.

Take pictures...here are some of mine on this old thread...

1992 300D no reverse

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)