Well, my Montero continues to kick me in the a**. It rans great after the engine rebuild, but it had a constant antifreeze smell after operating for long time. Checked all the hoses and connections - no leaks. Looking around some more, I discovered a puddle of coolant inside of the V. I suspected that it was coming from a water pump connection (known leak prone spot) and I thought that perhaps I damaged the o-ring or didn't seat it well during assembly. This weekend, I took off the plenum, fuel rail and intake manifolds to get to the central coolant pipe. To my surprise and disappointment, the o-ring was not damaged, so I started looking around some more. To my dismay, it appears that the coolant is leaking at the head gasket on both sides of the engine near cylinders 3 and 4 (see photos). I'm trying to decide what do to with this beast.
Option 1. Get OEM head gaskets (current ones are not OEM. I'm pretty mad at myself for this) and replace both sides with the engine still on the vehicle.
Option 2. Use some sort of Bars Leak product to try to seal up the leaking spots. They seem to make a specific head gasket sealant.

I don't really want to pull the engine out to replace the head gaskets. That's why I'm leaning towards doing it on the vehicle. Anyone done this before? It seems a pain in the rear, but doable. I'm not at all familiar with the coolant stop leak product, so I don't know if this is a good option at all. Please sound off on these options and give me your honest opinion.

 

I'm not too familiar with your engine overhaul thread but I'm assuming you had the heads shaved when you replaced the head gaskets? If so, aftermarket shouldn't matter too much, my old engine had felpro headgaskets and I didn't have a problem in the 80K miles I ran it.

As far as doing it with it in the truck, IMHO the hardest part is going to be reaching the crossover hoses and clamps on the back of the engine, It is definitely doable though. When I first got my sport, I had to change the heads because of bent valves, me and my dad, knowing absolutely nothing about these trucks, did it in a couple days with the engine still in.

 

I wanted to post an update on my coolant leak. I talked to my mechanic and showed him the photos of my coolant leak. With it being such a small amount and only to the outside (not into the cylinders) he suggested to use Bar's Leak instead of pulling heads. I was able to find two new o-rings for the larger coolant pipe, but no luck with the small o-ring that goes on the back of the water pump. After reinstalling everything I added a can of 2X Bar's Leak to the radiator (https://tinyurl.com/cb5azchs). When I started the engine, I can right away see coolant pulsing out of the back of the water pump. Stomach in knots and I'm nearly ready to pull my hair. Went for a drive to warm up the engine (as per instructions). When I returned, the coolant pulsing seem to have diminished. Hopeful sign. Over next few days of driving the leak stopped completely and the engine valley is dry. I've driven over 1k miles since completing the work and all is holding well. No overheating, no coolant loss, no coolant smell. I think I've dodged a bullet here.
If anyone works on your water pump, remember that little o-ring is a funky size. Do not loose it. It is a standard diameter, but much thicker than what you can readily find. I have not tried to make a custom o-ring for it, but it is an option I suppose. I think the only place to get it is directly form Mitsubishi.

 

The part number for the O-ring on the backside of the pump is MD030763. I have 4 extra O-rings if you need one, I can mail it in an envelope. I also managed to find some in a hardware store but I can't remember the size. I'll need to get my digital micrometer out and measure one.

EDIT:
I measured one of them and got the following:
ID: 15.45mm
OD: 22.10mm
CS: 3.45mm

The closest size I could find on a chart was:
(ID):15.47mm
(OD):22.53mm
(CS):3.53mm
or in inches
(ID):0.609
(OD):0.887
(CS):0.139

 

It is a good idea to have a couple of them on hand. I need to remember to order couple spares next time I'm getting Mitsu parts. Thank you for the part number. I've gone to two local parts stores and a hardware store looking for replacement. They all had the right diameter, but not the right thickness. Anything that was the right thickness was too large diameter.