Its a SLXI-DRC without the DEF system. So couldnt be that. Also I don't think it would be a mystery if we ran units that constantly stunk on regens. lol
A skunk perhaps. Dairy products will smell if something was spilled inside the reefer yogurt is bad, but if you wash it out it will disappear, who knows these days what some people do if the driver happened to upset someone and they went and put a few shrimp tails in the reefer engine compartment that will stink like crazy too.