Genltleman that I did some work for has 3 DT360's.... His were early production, but had no liners....when they were due for overhaul, the blocks were sent to IH or Navistar (I don't remember who...it was awhile ago), and the engines replaced. I have not worked on more than one or two and did not do the overhauls, so I said "to my knowledge", which may be wrong.
What's the Model and Code of the Onan?
Most common form that age was the CK and CCK, Parts are availiable, but getting expensive. If it's a J series (JA, JB, JC, JE), Parts are readily availible, you just need to know where to look and have a large checkbook (Cummins thinks that the old Onan stuff it worth it's weight in gold). If it's a CW series...Sigh...Then you need to see if it has Cotton or plastic insulation on the generator wiring. If it's cotton....nevermind...if You have a CW, let me know (I have one that is good for engine parts only) . Engine parts for Cw's can be had by getting to know your local machinist very very well and by finding an old timer Onan parts man who enjoys his job. All of these were made 40 years ago (these are the smaller Onans), the CW was being phased out, the CK series had something like a 50 year production run, and the J series was built from the 50's to the early 90's.
I have spent too much time with these. I have to go and rewire a control box on a JC tomorrow that caught fire. Nothing like keeping 40 year old equipment running in daily service.
Everything you ever wanted to know about old Onans:
http://www.smokstak.com/forum/forumdisplay.php?f=1
Paul