1983 gas furnace. Had to replace the limit switch 4 times in past 5 years. Some of the flames change from blue to yellow after the blower kicks on. I suspect leaky heat exchanger. Should I replace the exchanger? Model No. 867.769234; Mfg. No. SUGK100AH02. Can I do it myself?

Why replace a eat exchanger in a 28 yr furnace. Time for a new higher eff one. Price of a heat excanger and labor to install not worth it.

Joshdta: thanks. Any idea on what a reasonable cost range might be? It's a 4-bedroom, 2-story frame house with basement, built in 1938.