We've had our coolant tank replaced 4 times, the first two were under warranty, the third I paid for and the fourth was just recently. Apparently there was a bad batch and hopefully I'm done with it.
This was a Monaco priority part as we have a Roadmaster chassis. Thank goodness Monaco is still in business as we might have had a problem.
The problem with the first two tanks were that they lost pressure from the cap. The third tank had bad fittings at the top where the brass fittings were imbedded in the tank. It looks like the 4th tank was done correctly.
Good luck, I hope that it is a Freightliner part.
MM.