I have a 2015 lml Duramax I bought it July and it has 45,000 miles I noticed the upper radiator hose is hard when driving.... but soft when it cools down. There are a lot of posts about hard upper radiator hose and head gaskets. It runs fine and doesn’t blow smoke from the exhaust engine temps is good too is this normal there’s a thermostat in the upper radiator hose and I’ve always thought it was spossed to be hard. Could it be a egr issue? Also they just fixed the PCV seal and I noticed oil on the intake just before the turbo, any input would be greatly appreciated. Thanks!!