the heater core on my 1990 765T failed a year ago. I purchased a new core, c. $105 from FCP of Groton, and spent a weekend to complete the job. Independent garages hate this job, it's so labor intensive and may charge $500-$800. In all, I spent about 12-15 hours completing it. It's not that hard, if you're a contortionist! The dash and disassembly sequences will vary by year and model, but you basically can start near the center console and remove radio, trim work, ductwork to burrow into the interior of the firewall, where the heater core is positioned. There's debate about whether you need to remove the full dash; I did not. Be very orderly about removal, and study each piece and its interconnections to judge whether it really needs removal to access the core. Makes notes as you go, maybe take digital pics, and line up all the removed parts in your trunk or such in the sequence of removal. Put fasteners in ziplocks with their associated part. Have a good collection of torx bits, screw drivers and 1/4 drives, extensions, etc. the actuall R&R of the core itself is easy, but getting in there, and re-assembly is the time consuming part. Judge your success by the number of leftover parts and busted shards of plastic. Popping the plenum enshrouding the core apart was one of the hardest parts. good luck. chris in vermont, 244, 765, 945.