It is the power steering fluid reservoir on a Freightliner truck and has a crack at the filler neck, where the neck transitions to the body. The good thing is that there is no standing fluid at the crack, just splashed fluid when the truck is moving. The crack is not visible in this photo. The tank is made of a translucent white plastic and I don't know whether it is ABS or nylon or what other kind of plastic it is. I don't see any markings indicating type of plastic. I don't even know if it is themoplastic ot thermoset.
A new tank is $180, the cheapest used one is $150, hence my effort at repairing the existing tank.
The two options I am considering are
1) If thermoplastic, I can try welding with a soldering iron.
2) JB weld for plastic, after cleaning and sanding the surfaces.
Any suggestions are most welcome.