Coolant and oil leaks at the rear turbo? It's a PITA to do anything in that area, and fingers crossed, the turbo is in great shape. I would take off the turbo piping and inspect the turbo for coking and signs of physical damage. Same for the front, even though it seems to be working ok currently (?).
Definitely try Z's suggestion of topping up the coolant to just beyond the FULL line and watching it over a few days. Run the SHO enough to get the coolant circulating, a 30 minute drive between each check should do it. If the coolant level does not go down, it is unlikely that there are air pockets. As long as the engine temp behaves normally, you should be OK.
Seat heat IIRC is provided by a thermoelectric aka Peltier device, and has nothing to do with engine coolant based heat. It is kind of subjective how much heat the device produces, but quite a few have said that the MAX setting would produce a "burn" level of heat on the hind quarters. If the seat barely gets warm on MAX, check the fuses, and if they are OK, very likely the heating element needs to be replaced.