1990 Ford f450 transmission massive leak, do I need to rebuilt it?

Ok, I got a 7.3 Ford f450, 1990, i just bought it, two days after the transmission started leaking pretty bad, I need to know if my transmission need to be rebuilt, as what a mechanic told me, but I'm not pretty sure because if I put transmission fluid into it it will drive and shift perfectly until it drains again at this point I need to refill with more fluid, is this normal for a transmission that need to be rebuilt?

Also it will leak even when is not hot, as if I pour in the fluid it will almost immediately start leaking

I would make sure that all of the transmission oil pan bolts are tight. If someone changed out the filter and didn't torque the bolts properly, or over-torqued them and warped the pan, it can leak like a sieve. The rear housing adapter might be the source of the leak too. I'd just take it to a shop for a good inspection up on a lift and see if they can fix the leak without doing a rebuild. If it otherwise runs well and shifts smoothly you probably don't need an overhaul yet.

Stop the leak! Replace the seals and the pan gasket! Make sure you are checking the fluid level with the engine running before adding more fluid!

As long as the fluid remains topped of it might not need to be rebuilt. Find local shop at ATRA.COM for estimate to repair. Leaking that bad its either the front seal (transmission will need to come out to replace that) or a cooler line leak

Find and fix the leak.

A leak like that is probably an ATF cooler line. By now you've damaged the clutch packs in the tranny because you were dumb enough to keep trying to drive it and ran the transmission out of ATF.

You've screwed the tranny up driving it like that. Go get it rebuilt.

WHERE is the leaking fluid coming out?

The transmission (bottom) pan?
The rear seal?
The front seal?
A cooler line?
Somewhere else?

Tell me something more and I'll let you know what i think about it.

-General automotive mechanic since 1972. Retired in 2018.