I have a tank off a radiator right now. In my opinion, the wall thickness is inadequate to tap. You need a fitting with a head on it (similar to a metal valve stem) that would be supported from inside the tank and could be secured with a nut on the outside. You could run a wire in through the vent nipple and over to the upper hose port to pull the fitting in.

I like being able to rely on my car to not break down/leave me stranded, so the only solution in that case would be a new radiator.

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Agreed. I just contributed $200 to Nissens bottom line for that very reason.

Why can't he just JBweld this as others have said before with the epoxy? I did that on a 300D radiator that then did not leak for a further 10,000 miles until I sold the car. Worked just fine, radiator repair is specifically what some epoxies, like JBweld, are for.

My crack was larger, on the opposite side and caused by the oil cooler mount.

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Amazingly Land Rover has the exact same design - plastic nipple on the top of the radiator that breaks if you look at it funny. So far reading through the posts on that forum no one there has figured out a good way to fix it either. Everyone says just bite the bullet and put in another radiator. Drives me crazy.

there are two types of epoxy for sale at most mcparts stores. One is the radiator tank repair for 20.00 the other is the two part syringe plastic epoxy. 4.00 I cheaped out and used the syringe stuff. it's held tight for 2 years now.

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Ive had success in taking the radiator out and doing this fix with the radiator sitting at a 90 degree angle .A small pipe with one end treaded ,the other a nipple for the hose ,Any car -parts store should have it .Ill drill the opening for the treaded part,then set the radiator at this angle with the hose /pipe slightly up and pour in a 2 part epoxy after mixing,this liquid mix will surround the pipe making it bomb proof.The 90 degree angle is so the epoxy fills up around the pipe ,makes a nice pool around the joint .