core is out

i took my heater core out the arm had a crack in it but it was just a platic extension i ran water through the core and no blockage the metal is all solid no soft spots no cracks or leaks is the heater core still good

Yes. You can replace the plastic tube with (4) 45 degree copper elbows and small pieces of heater hose. I did one of mine years ago. You can get the elbows at any hardware store. There are cheap, like $.50 each. Take the old tube with you to match the size. I think I used 1/2 inch or 5/8 on mine. You will also need a short piece of straight pipe on each side. As I recall the two sides are different diameters. This repair will save you about $80 Good Luck.