Replace, these are not your grandfathers rads, they combine the normal metal with plastic end tanks moulded together. Back in the day our company did work for Johnson Controls and an engineer told me they were working on making these hybrid tanks and said others were laughing at them, guess whose laughing now?
Tanks are available used and new, not too many have been mentioned failing on this forum so used ones from eBay may be the way to go.
Basically drain the system, undo the hose clamps, remove two rad clips and lift the rad out. Easy peasy if you have the tools and the time.