Coolant reservoir deteriorating

[mxlucey]

So on my 2002 ranger 2.3 the coolant reservoir has gotten very soft not like squishy but I am able to scrape off the plastic with my nail. I imagine its time for a new reservoir but I was wondering what could be making this happen, excess heat? My gauge reads fine though it may be faulty is there a way to check?

 

[killj0y]

Could just be deteriorating from heat, the elements, other factors etc...did you buy the truck new? If not it could have already been swapped out with an interior unit.