Volvo D13 losing coolant

I have an issue that's been persistent for about 6 months now. I've been losing coolant at a rate of about a gallon a month with no visible signs of leakage, running about 8-12k miles each month. Until yesterday, haven't had any issues or codes except for one last month when the sending unit in the DEF tank went out. Yesterday ran hard coming home from La Vergne, TN to Augusta, GA and code threw which prompted me to do a parked regen. Regen went fine, soot level gauge went down to 0 and up and running again. Today I was concerned with this as its the first regen I've ever had to do since I bought this truck about a year ago. I drained my air tanks looking for leaks, no sign of water in oil at dipstick and then decided to take the EGR cooler hose off with the elbow and venturi tube. I noticed a large chunk of yellowish buildup clogging about 3/4 of the Venturi tube and buildup with moisture in the inlet of the cooler. I'm thinking that this may just be a bad cooler at this point and its leaking internally. North of the clog in the venturi pipe I noticed only regular carbon residue, nothing built up to be of much concern. I took a couple photos to help you guys out if you look and hopefully help me diagnose this because the shops I've asked are all wanting 1200-2000 in labor for this repair that I feel I can do myself if its just the cooler, even if it takes me the entire weekend. It does look labor intensive and I know I'll have a mess on my hands. What do you guys think? Truck is a 2013 VNM daycab with 640k on odo. Thanks for your help.

 

That's what I was thinking. I'm pricing parts now, planning on tackling this starting Friday. Thanks.

 

Thanks for the tips, and I wouldn't have thought to change the sensor just yet. What is the plastic connector to the block you're talking about? I've watched a few videos and haven't seen that part. I've got to be sure to have everything beforehand as the closet dealer that would be open on Saturday is 130 miles away and I really can't be down much. Thanks

 

Thanks for the parts numbers on those. Volvo and several other suppliers have that egr cooler on back order with an unknown eta but I was able to find an aftermarket one online. Another question though, I have sourced the additional parts you listed bit can't find the part numbers on those o rings for the plastic connectors, you wouldn't happen to have an item number on those would you? Also was thinking about getting the turbo install kit #85116577 it has the bolts and washers/ seals. Would that be okay? Thanks in advance.