Oil out the bellhousing is usually the rear main seal on the crankshaft. Replacing it might help, but doesn't always. You should be able to determine if it is
oil or tranny fuid, as they are significantly different in feel as you rub your fingertips together. The truth is, more cobras leak a little, than none at all. Some hemmorage
oil out every possible place, they are called FE's.
When you say "rear gearbox" do you mean the differential? Most have a breather that can allow some oil to vent out, normal to run a length of hose from the breather up and loop it over, it will prevent most blowoutof gear oil. You need to determine where the fluids are leaking from before trying to fix any of the leaks, the best way is with flouro dye and a strong blacklight. You may be surprised what is leaking and where it is leaking from.