i don't mind heater cores, one helped me nail down my current job :D i came in before i was hired and worked, there was a 2000-ish taurus with a heater core that needed to be replaced. it books out for 6 hours due to removing the dash, and the manager (another master tech) had done a few and knew about how long they take. when i started i asked if he had ordered the part yet, and he said he would get it for me before i needed it. an hour later i handed him the old one and he just stared at me like this :eek: and called me a freak of nature...and then ordered my part.
more on topic, i haven't done an xj/mj heater core yet, aside from pulling them from trucks i'm parting out.