It's a very easy job to pull out the radiator on these 240's, so I would do that and take it to a rad shop for a flow test. My '83 was 50% plugged with scale deposits, despite a flush and fill every two or three years. They disassembled the (all metal) rad, rodded out the tubes, and reassembled, also repairing a pinhole leak in a tube. The flow test after this work was pretty convincing. They just stand it on the shop floor, fill it up then unblock the outlet and let the water run out under gravity. Much bigger gush than before. Cost was $85. Decent quality new rad is about $60-80 more. Use new hoses when you reinstall - cheap insurance.
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Bob (81-244GL B21F, 83-244DL B23F, 94-944 B230FD)