Allison oil leak advice

[TwelveVolt]

I would appreciate some input before my next shop visit. At this point, it is only at a nuisance level, creating soot in the engine compartment and a light film on the toad bumper after a long trip. From the oil pattern, I am guessing it is the gasket of the fluid pan. None of the fluid levels (oil, ATF, hydraulic) are noticeably dropping, so I am assuming this is the source of the residue. Would torquing the bolts be a reasonable first step?

[Old Scout]

...you didn't say what model/year of coach or engine brand but two things about Cummins engines: 1-circa 05-07 engines have a slobber tube over the starter--if you slightly overfill the oil, you get some "slobber" in this area; and 2-many Cummins of varying ages have issues with lift pump leaks--also located above the starter. Point is--its often hard to determine the sources of the leak. Example: the local Cummins shop who I have trusted over the years diagnosed a leak in this area as an engine rear main seal; turned out it was the lift pump leaking.
PS--careful on torqueing anything--Allison housing is all aluminum.....

[TwelveVolt]

A misdiagnosis is exactly my concern. This is a Cummins ISC on a 1998 Spartan chassis.

You are suggesting that the oil may be coming from above and working its way forward (right) on the transmission instead of out of the transmission and back (left) as I had assumed.

[dbarton291]

It the problem was the gasket between the control module and the main case, you wouldn't have all that oil residue on the torque converter housing. That's coming from above and left(engine side) in the picture.

[Old Scout]

Yup--as I indicated, more likely its from the engine.....oil or fuel--interesting, but even diesel looks a lot like oil once it washes down across the dirt, grim, and old oil on the side of the engine block....

[TwelveVolt]

Thanks for all the feedback. I have been leaving maintenance down there to others lately. Now that you mention the slobber tube, I am pretty sure I had one and I don’t remember seeing it when taking these pictures. Where does it attach?

[Old Scout]

...it attaches at/to the valve cover but more importantly, where does it terminate? The "slobber" tube on my 2003 ISL400 terminates by the oil filter so I get some oil spray there. Newer "pegasus" engines terminate over the starter. Not sure where your older ISC terminates. Again, the new ULSD is hard on lift pump gaskets.....