Originally Posted by Aquabelle
Your HX shouldn't need replacing: just clean it in situ unless when removing the end-caps, the tubes appear very badly clogged...in which case remove the whole thing and take to a radiator shop for cleaning and pressure testing.
I dunno Aquabelle.
Unlike an engine HX, a failure to a transmission cooler can be quickly catastrophic. Our two were just replaced ( 10 years old and in salt water all their life) with parts less than $200 for each one. On a newly acquired 15 year old used vessel and not knowing how the PO treated things, a replacement TX cooler is worth considering.