In the '80s my truck was looking really ghetto, no front bumper, grill or pan... no license plate for like 15 years. I had rocks put pin holes in the rad a few times. It's more of a hassle to pull it and put it back than to solder the holes shut. One time it started steaming on the freeway. I made it ten miles home with shit all bubbling and hissing. A pretty good crack in a seam on the upper part. I didn't even pull the rad out... drained the coolant and torched the fuck outta it in place! Bake it dry with a torch, try to clean the joint, hose on flux and 50/50 acid core!!! Ran for years Ratsun as hell.
A while back I put a fresh head on the L16, so I figured I'd get a new rad too. The old guy at Beaverton Radiator wanted $375 for full-on, hot-set-up re-core job. He said it was not the OEM rad and that it was "rotten" and not worth fixing. He said replacements for the L16 are not available, only L20 rads. The difference is the top inlet is on the other side. You have to use an L20 top hose for the shape then cut half of it off. I think I had to relocate two of the mounting holes too.
A Ratsun Bro gave me an OEM L20 rad that was in great shape. I change my coolant and flush the system about every 4 or 5 oil changes. I would consider having an OEM L20 rad re-cored. Rather than the new unit he showed me lookin' kinda sketchy. I remember shopping for aluminum rads and you can send dimensions/drawings to get a totally trick Griffin racing radiator for about $400.
When I swapped the L16s 35a alternator for L20s 60a... it's a bigger unit, so I was considering have a radiator made so that the lower rad hose wouldn't hit the Alt/Fan. It's a tight fit, but I made it work. Couple zip ties on the hose to the frame... Ratsun.