I would try soaking the heater in pure vinegar, & if that don't work something stronger like CLR or muriatic acid. Make sure you rinse really well after. I would also bleach it to kill off any algae/bacteria/parasites. <1:10 overnight.> Rinse well after bleaching (last one with a double or triple dose of dechlor.)
As for the airline, I would replace the tubing. I am pretty sure that there is a way to change the tubing. If all else fails, you can cut the tubing off close to the pump & join in a new length of tubing using a straight connector.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.