I DIY'd the tank on my "spare" 77 240D as well. It was leaking badly at the top tank to core joint( the lady who owned it I guess kept adding water) so I unbent all those brass tabs, reamed it out and put it back together with some non-hardening Permatex. Good as new now, I think. No leaks and runs cool. It can be done.

Rick

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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 (??)