Looking for a replacement lower unit for my 1977 Evinrude 55 HP, drive shaft is 20" to top of pump housing. What year models and HP might be compatible? I see a couple out there, but welcome any others. Already repaired a hairline crack, don't see evidence of leaking but still taking on some water, now gears are popping so I'm assuming prop shaft seal is compromised, possible bearing and/or gear damage making further repair impractical.