An injector line leaking is poor terminology. Unlike many other engines there are no injector lines, not even for a return line. There is a gallery [hole] in the cylinder head that not only feeds the injectors fuel but is also the return line for the excess that the injectors do not use. There is one external feed line from the PT pump to EACH cylinder head connecting at the cylinder head front. There is one external return line from EACH cylinder head at the back of each head.
No internal line that can leak into the engine.
To be fair he simply could have been talking the way many do about what he works on mostly but still know that those engines are like that and somewhat different.
Now the seals around the injectors could fail and leak fuel or coolant, either into a cylinder or into the valve cover area.
Do check for a hydrolock which could jam the engine/starter. Bar the engine over. The barring attachment should be right next to the PT pump.
So I'm going to suggest that you go to BOATDIESEL and join. Look through the PDF file [L.H. menu on the main page] section for:
Find: ASSOCIATED PRODUCTS
> Section. > Click ENGINES
>Sub Section. >click Cummins
>Products > click V555M
That will bring you to the V555M.
Look at the L.H. side of each listing and you will see [light lettering 14 - 19]
a series of sections 1 -5 of the V555M owners manual which describes a lot including the valve and injector settings and HOW to do it. Read it over.
14 -18 are the manual, 19 is the parts book.
Note these cover the natural mostly and a couple other engines so be carefull you understand which engine is referred to..
You will be allowed to download one section at a time, per day, as a level 1 member. They each are 6-10 Gbytes so take a while. Level 2 member more.
Find the barring description. Bar the engine over, not difficult but slow.
There should be compression resistance but that will release as you keep pressure on it and then it will carry on to the next cylinder. It will simply slow you but not stop you. Do two full rotations. If one cylinder is hydrolocked it will simply refuse to allow any further rotations, at least for a long time.
The barring description starts in section 3 so download that first.
Check the starter motor though as it could have developed a dead short which could prevent it from even attempting to crank the engine but also put a huge load on the batteries and cause a BIG Vdrop. A bearing could also have jammed preventing the starter from turning and creating the Vdrop.
I hope for your sake it is the starter. Not that the other isn't repairable but a starter will be a days job if access is reasonable. It is heavy , about 60 or so lbs so be sure you have control of it. You will need a LONG extension and 1/2" drive handle. If memory serves the socket will be 9/16 or 5/8. Upon more thought?? may it's 3/4". Easily checked as two of the securing bolts are accessed easily, it's the one behind the long extension is required. Some of those big old starters have a removeable end cover separate from the bearings which can be removed for brush access. THat could also enable you to try rotating the armature as a rough check if it is jammed. Don't know what you have now as many have had replacement starters over many years but take a look.
Diesel in the oil can be checked with an oil test.
Get an oil test kit and send a sample with a note that you are specifically concerned about diesel fuel in the oil and ask them to E-mail or phone you.
A redneck way [courtesy Ski in NC] is a drop of oil on a white paper towel. If only one dark ring shows it's oil, if a second much lighter ring shows there is diesel. It's not conclusive but indicative.
Enough for tonight,
This link may get you closer without all the button pushing.
If not then you will have to go through what I outlined above.
Link:
http://boatdiesel.com/PDFLibrary/Search/index.cfm?ProductID=4491