Actually the old green Sears jacks are pretty good !
NEVER saw a green sears jack... when did they make them??
I don't know when Sears started to make green jacks...
...but I bought this one new from Sears in 1976 as one of the first pieces of my shop equipment. It still works flawlessly over 35 years later.
hickmlg09, mine has many similarities like the one your dad has now.
I'd say it's almost the same shade green with white, the same silver foil label on the lift arm describing the weight capacity, the same location for the data plate, riveted on the right side of the frame etc. Yours is a different design jack and mine is only 1 1/2 ton capacity, but I bet the same manufacturer made them both.
Sears didn't make their own equipment back then, but bid it out to different manufacturers.
Here's a suggestion, buy your Dad a new low profile jack, he deserves it.

Then snag his old one and take it to a competent repair shop and get it repaired and then keep it for yourself for the next 35 years and think of dear old Dad every time you use it. These were made out of material that still could be welded and repaired.
Hiball should be able to supply you with any parts/seals needed for the hydraulics part of it should you need those.
BTW, when looking at flea markets, look for
green Craftsman jacks.

They are pretty good pieces of equipment.
Oh, one thing more.....don't think just because something is old it needs to be replaced...
...here's an over 70 year old Walker floor jack I restored...
...and I bet it out lives you and me both.

Good luck and it sounds like your Dad is pretty lucky to have a daughter that cares this much. Way to go!
Thomas from the
Restored 1930's Auto Shop
http://www.garagejournal.com/forum/showthread.php?t=51567