Re: 2003 Mercury Lower Unit
Your OEM part number is 821306T6. If you do a Google search of the part number, you should come across a website that offers a very big list of lower units that that part number will fit.
Here is a very small example of it:
1998 1031203UD Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1999 1031203VB Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2003 1031207AF Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1998 1031207UB Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1998 1031207UD Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1999 1031207VB Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1999 1031207VD Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2000 1031207WD Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2000 1031207WF Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2001 1031207YF Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2002 1031207ZF Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1998 1031213UB Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1998 1031213UD Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1999 1031213VB Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1999 1031213VD Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2003 1031217AF Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1998 1031217UB Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1998 1031217UD Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1998 1031217UF Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1999 1031217VB Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1999 1031217VD Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2000 1031217WD Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2000 1031217WF Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2001 1031217YF Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2002 1031217ZF Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2003 1031301AD Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
1998 1031301UD Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2000 1031301WD Gear Housing(Propeller Shaft)(2.00:1 Gear Ratio)
2001 1031301YD Gear Housing(Propeller Shaft)(2.00:1 Gear