The place you are looking for is at Kurnell in Sydney, on Cook Rd.
Rent is cheap, has power and water, plus Russel the owner is great for advice, or can be contracted to do some work for you.
I am currently there myself using the facilities.
Mate I know it is not Shell Point, as this is near to Taren Point. This is not a slipway though as per the previous reply, you will need to have the boat towed there. This makes sense only if you are looking to do lengthy repairs.