Re: Impeller Question
18-3217 if it only needs the impeller and gaskets. You can order from NAPA by that number. Around $45.
18-3320 if you need the housings too.
If the little white plastic guide tube is melted you will probably need the housings too.
Anytime you pull any part of the drive complete or just the lower (like for impeller service) You MUST put the shift lever in Forward gear.