Leaking from bottom of radiator from where the plastic meets the radiator. Does it usually mean you have to replace the whole radiator or can you just replace the cap or the seal. I have a F-250 powerstroke 4x4 2005.

The whole radiator needs replacing. When refilling, the ideas in this link may help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-10.html#post1923468