A competent radiator shop can replace your side tank for a reasonable fee. I would recommend replacing both side at the same time - if one side is cracked, the other isn't far behind. I recently replaced both of my side tanks. I think they were around $20 a piece for parts. I don't know about labor as I replaced them myself at my shop.
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Current mods: 350 TPI engine, SLP headers, Flowmaster exhaust, Hypertech chip, March underdrive pulleys, Hurst shifter, aluminum driveshaft, Spohn adjustable LCAs, wonder bar, and panhard bar, LS1 rear disc brakes, Zexel-Torsen HD diff (T2R) w/ 3.42 gears, ARP wheel studs, Summit aluminum girdle diff cover, Koni "Yellows" all around, a few Auto Meter gauges, and a heavy right foot.
Current project 357c.i. SBC: 350 Vortec 2-bolt main block with Eagle Splayed 4-bolt main cap conversion (powder coated black), ARP main studs and bolts, Eagle 4340 Forged 3.500" stroke crankshaft, Eagle 6.000" H-beam rods, King Alecular rod and main bearings, Durabond Teflon coated cam bearings, Trick Flow (Arias) Forged 4.030" flat top pistons (Swain GoldCoat and PC-9 coated), Total Seal gapless rings, LT1/T56 flywheel (neutral balanced), TCI Rattler 2000 balancer, Edelbrock 2-piece timing cover, Comp Cams Hi-Tech timing chain, all completely balanced and blueprinted.
Overkill? Yeah, probably... | 
