Burning oil after new head install

[IrishKW]

Need some input on why I would go to burning 1 gallon of oil every 3500 miles after a new head was installed.

2007 CM870 8520cpl

Took to a local shop because I had a miss and was pushing a little antifreeze out of the cap, passed a cutout test so they pulled the injectors told me there thinking was bad o-rings. Injector cups were leaking antifreeze, so they installed a Cummins reman head, plus new cams and rocker arms. It had a oil leak on the front cover before and only used a half a gallon of oil in 18,000 miles. As soon as I got it back it was burning oil, you can smell it in the exhaust. Now that shop wants to charge me to diagnose the problem and said no warranty on labor only parts. It took them over 50 hours of labor last time plus I was down for 3 weeks. I told them I can't afford for them to work on my truck! And they never did find my miss, I found it myself with a injector leak test I learned on this forum.

Wish I would have found this forum before I bought this truck, I have ran b model cats the last 20 years and always did my own mechanical work, even rebuilt injection pumps. Probably would still be running them but the company I'm with wanted me to go to a elog compatible truck. Found a 2007 T600 set up like I needed supposed to only have 200k on overhaul and transmission and price was right, thought I'd give Cummins a try.

I checked the turbo, no oil on either side. Can oil get in through an injector? Could a valve guide seal possible be defective on a new reman head? Going to start taking it apart to replace the injector. Just needing input on what I should be looking for.

Thanks for this forum, I'm learning a lot about these red motors, for a while I thought maybe I just needed to get some yellow paint :confuse: