The only easy fixes are a loose hose clamp either on the top or bottom of the radiator OR a loose drain cock (either the stopper or the whole assembly itself). You'll be able to tell in 5 minutes if those things are all OK.
Beyond that anything you do is a temporary fix, at best. You could try to find where its leaking and resoldering it yourself, but in my experience those repairs never last. "StopLeak" additives are a definite NO.
Depending on your area recoring the rad may be an option (it was $500 near me, but others have said recores are $100 in their parts of the country). You could also find a way to use a radiatorbarn.com replacement, but it'll take some modifications because they don't have them for the diesels, I think.
i used a modified 3fe rad for my 2h. i dont know if this would apply to 40seires, but couldnt you find a 2f 40series rad and see if it can easily be modified to you application(if you can find one in good condition)