[THEFERMANATOR]

Service life on any timing chain should be 150K miles. And some of em do get run hard, and wear out the bottom ends. I tore one apart with 182K on the clock, and it still had the factory break-in coating on the bearings. They don't take well to not haveing oil changes done religously. I personally like the 91-95 4.0's myself, but that's just me. The 87-90 4.0's seemed to hold up the best though, mostly due to the lower HP rating(plus the old style ones got better milage, I got 20-22 on my trip to TENNESSEE this year with my 88).

And for your water leak SPARE, check the seal on the water drain tube for the evap. There is a connected tube that runs the water down from the A/C condensation, but rain water can run back in em. And like FRANCO said, check your outside air intake.