Old Cat 12 Motor Grader Pictures

That would be an 8T model, 1951 vintage, D318 engine.
Where exactly is it leaking?

I read tag as 8T6607

If there's a oil leak at the rear somewhere I'd bet the engine was leaking oil and dropping down onto the tranny/rear end and then onto the ground, looking like a rear end leak because as already stated the tranny bolts directly to the engine w/o a driveline.

I see from the pics it also has the typical steering gear box leak. I've seen very few 12s that didn't leak there to one extent or another.

Hi, 657Bruce.
Neat find. Thanks for sharing. CCJersey is right in that there is no differential in those old Cat rigid frame graders. How-wevver, there ARE some places where it could leak oil around the back end. The 'tranny' IS bolted directly to the engine but there is no direct connection between the engine and the crown wheel housing. The power from the engine goes forward through the clutch to the transmission. There is quite a substantial drop from top to bottom of the transmission and the transmission output shaft goes directly into the crown wheel housing at the back of the lower end of the transmission. There is a large plate covering the entire back end of the crown wheel housing and the gasket under that plate has been known to leak sometimes.

It is also possible, as Ol Grump mentioned, that the engine has an oil leak which is dripping down over the crown wheel housing but this oil would most likely be BLACK and would show up on the TOP of the crown wheel housing where there ISN'T any place to leak.

There are also seals at the outer ends of the axle housings where the tandem cases attach and these have been known to leak. Before making any 'rash' moves, I'd suggest going back there with an inclinometer, or a Quicksight level with Vernier grade setting on it and check the tops of each tandem case to see if they are pretty close to even. If one has a distinctly different reading from the other, there is very likely to be a problem with the inner bearing, sometimes called the 'square' bearing, of one or the other. Another clue for this is if the tops of the tires on one side appear to be slanted in towards the engine rather than parallel to the side of the engine.

Another possibility is that there may be a crack in the crown wheel housing itself - rare almost to the point of being unheard of but there is almost always a first time for something to happen - and any oil coming from such a crack would hardly look like engine oil, more like heavy gear oil.

As Ol Grump said, it is not uncommon for those old power steering units to leak - no big deal. I can't see a control lever sticking up for a hydraulic side shift and it still appears to have the old mechanical lock on the side shift so I'm guessing it doesn't have the power blade attachment.

All models of these old Cat 12's were good solid machines which gave little trouble, especially when you consider the work that many of them were thrown into. A LOT of them were expected to do the work of a D9 as well. (Well, maybe only a D8 'cos nobody outside of some of the Cat design team had any idea what a D9 might be able to do back in 1950-51.)

Just my 0.02.

Call up local metal recycler (scrap yard) and get a quote for complete machine less disposal of tires (ask about this, don't want to be caught unaware of this if they won't take machine with tires on it or if they charge you a disposal fee.

Anyway, when you've got the quote, you can translate it into the amount you could potentially recover from the machine by simply dropping it off at the yard. If you are bargaining with the present owner to purchase a non-operational machine with "known" problem of leaking so badly from the rear differential that it couldn't be used any longer, you should conider the cost to load and haul the dead machine away and take that off the price quoted at the scrap yard.

The grader should weigh over 11 tons as it sits.