Leaking coolant

If it is directly behind the mount it is likely the core plug that is rusted through. If that one has failed the others may not be far behind as well. Replacement isn't that hard on those. First you need to drain all of the coolant. You next attach an engine support or cherry picker to the engine, then remove the frame side of the engine mount, then the block side. With those out of the way you can access the plug. If you use a dull punch or drift and tap one side of the plug you can usually get them to loosen up and twist sideways so you can pry it out. Then you scrub the hole with a piece of scotch brite to remove any corrosion or other debris. Wipe it all clean and then drive in the new one with the correct driving tool or large socket. It needs to go in nice and square or it will leak. Once installed you reinstall the mounts and refill with coolant.
The thing then is to look at the plug really well to determine if it rusted from the inside or outside. If it was from the outside then you will want to inspect all of the rest. If from the inside you may want to replace all of the ones you can access now.