i'm new, but happy to be here. i'm actually not currently a volvo owner, but have been in the past and am looking for the right opportunity to become one again. anyway, i have a lead on a 740 and have been doing some research on this site to get a sense of common problems, fixes, and the like. i have read several times of the headache that is involved in replacing a leaking heater core. so my question is: do all heater cores eventually leak and need to be bypassed and/or replaced, or does that disease affect only a lucky few? is there a common mileage where the leaking starts/occurs? what i'm really getting at, i suppose, is whether it would make sense to pre-emptively replace a heater core before it even starts to leak, such as perhaps in the spring/summer when i have more time/better weather/don't need heat, such as to avoid having to pull carpets and wipe up coolant, etc. etc. any thoughts?