Removing fuel tank
Yes, your tank will fit through the companionway, I've had mine replaced. I'd recommend you call Pacific Seacraft to discuss a fiberglass replacement for yours while you're going to the trouble. When seawater is in the bilge, corrision can setup between the keel bolts and the aluminum tank resulting in the leaks you're experiencing. I think staying with aluminum is not worth the risk and future hassle. You may want to have your boatyard evaluate the health of the keel bolts as well since these can also be affected by the same corrosion process, and I'd at least clean the bolts/nuts up good and reseal them before installing another tank. Be sure to thoroughly clean the bilge compartment with a degreasing cleaner if any diesel has been sitting in the bilge, else you'll be smelling diesel for quite a while. I'd also replace all the related hoses while you're at it since the old ones may be saturated and also contributing to any diesel smell below decks. Finally, its also a good time to put in a new engine fuel filter since you'll have to bleed the fuel lines anyway. Quite a few PSC owners have had to deal with this, so I imagine you'll get a few other helpful responses.