Troubleshooting root cause of oil leaking at shaft hub

[Toughship]

My boat is a Tiara 3500 with Crusader 7.4 engines and currently at a local marina for repair .  Port side has a vibration when taking it up to 3000 rpm to get on plane . Also spraying oil from the shaft hub where it bolts to the transmission.   Also spraying water from the dripless seal .   
    My concern is how can I be sure that the problem is properly identified ?   What step by step process should the yard follow , where do they start ?   Don’t want to get caught up in a repair by trial and error .
   Transmission shifts smoothly, no gear noise or overheating alarm .

[Tango426]

I would haul it out and then:

1. Check propellers. See if they need to be tuned. If they are old and in salt the may have leached and weakened. 
2. Check strut bearings…make sure they do not have any play. 
3. Check for the propeller shaft alignment with the transmission. 

Odds are something along that route will be the issue. 

My boat is a Tiara 3500 with Crusader 7.4 engines and currently at a local marina for repair .  Port side has a vibration when taking it up to 3000 rpm to get on plane . Also spraying oil from the shaft hub where it bolts to the transmission.   Also spraying water from the dripless seal .   
    My concern is how can I be sure that the problem is properly identified ?   What step by step process should the yard follow , where do they start ?   Don’t want to get caught up in a repair by trial and error .
   Transmission shifts smoothly, no gear noise or overheating alarm .

[Toughship]

Tango   Thanks for your reply .     The mechanic said he will also sea trial the boat to get a visual on any wobble of the running gear , meaning shaft and will also be checking for a bent shaft when hauled . At least he didn’t just say the culprit is a bad tranny .
    I just have to convince myself that he knows what he is doing and doesn’t take advantage of the situation .