Yes, replace the surge bottle, the plastic probably has a lot of minor cracks in it from the heat.
On my 2005 Fleetwood Excursion 39S with a Cat C7, the surge tank that sits on the top right corner of the of the radiator went in Billings Montanna last year. Luckily it was across the freeway from a Freightliner dealer. They had them in stock because a lot of them went out. They said the original plastic wasn't a good quality for the engine and water heat it receives all of the time. They changed it out and I went on my way.
Bill