I have a 2003 5.0 MPI with the alpha one outdrive. I am loosing gear lube (had to top off the gear lube in the monitor after only 4 hrs) but the lube doesn't show any sign of water, is not leaking in the bilge, and didn't leak on my garage floor after being stored there all winter. So I have a bad seal, but don't know where...What should I check and what seal kit(s) might I need (I'd like to have them in hand before I start taking things apart!). Anything else I should consider while I have the unit apart?".

If unsure then best to replace all the seals to make sure outdrive doesn't run low on lube and damage bearings and gears, also to make sure no water is getting into outdrive.

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there is definitely no water in the outdrive. Lube looks like new. This engine has the lube monitor - that's how I can see the level is going down. Someone today suggested that the elbow fitting at the transom for the monitor is plastic and tends to crack, which may explain the slight loss of lube without there being a bad seal. I can't tell for sure because its nearly impossible to get at that fitting, never mind to see it...

The Gen II has a seal carrier under the water pump impeller.
The gear lube passes through the seals into water pump and through
the engine and out.
Change the seal carrier as an assembly.
I would also change the shift shaft seal assembly. These parts are easy to change and not to expensive.
dean4now