[Kiwick]

If the convergence or purity is off it's not necessarily due to a serious fault in the set

Components like resistors and capacitors slighly drift from their initial value over the years, as long as they stay within their tolerance, this is acceptable and doesn't compromise their reliability, also the wirewound pots used in convergence circuits can drift off their factory settings over time

CRTs also get magnetized and this compromises the color purity (color blotches) so you should check your set's degaussing system and demagnetize the screen

I have an early 70s Philips delta gun set, when i got this set the convergence was way off but after some tweaking it came back to near perfect, and it's still there after almost 7 years of daily watching