I've got a D4-7U which I'm currently repairing, with a D315 engine.
 It seems to have got the old style oil filter, with a strainer and a paper filter inside if it.
It did not have any proper seals or gaskets on the filter housing, just lots of black silicone sealant everywhere.

Some questions:

• Where do I find the o-ring 6B7279? It goes between top of the filter element 4A332 and the cover plate 6B1852. Or at least having some specs for it would be good so I can look for a generic replacement.
• How do I convert to the fill-flow style filter that uses a newer filter element? New filter element 9F6700 in the catalogue, 1R0659 is the modern equivalent from the dealer. Parts catalogue seems to indicate I will need the new standpipe and new screws at the bottom to support it. Possibly get a whole thing from a newer parts tractor with a full-flow installed? 
  
  
  
  Here's some part numbers for my filter I have found out:
  
  Paper filter old style to fit inside strainer: 1R0729 filter
  Parts catalogue calls for 4A332, some googling have yielded that it's equivalent to 1S9150 and 1R0729 (latter one is a current part), so I'm good for filters.
  
  Paper filter new style full-flow: 1R0659 filter
  Parts catalogue calls for 9F6700, modern equivalent 1R0659
  
  Main filter cap retaining screw seal: 8F-9207 washer + 8F-9206 oring
  Old style copper washer was 5B-5961. Can be replaced with a newer style steel washer and an o-ring
  New style flat steel washer 8F-9207
  New style rubber o-ring 8F-9206
  New style flat steel washer was not available from dealer, but the o-ring was. I will find or make a necessary steel washer.
  
  Filter cap to filter housing body: 5B-5937 o-ring
  
  Filter housing body to filter base: 5B-5940 o-ring  
  
  
  
  
  

Check with ag-mike on this board. He wrote the book on converting the old bypass to full flow.
At one time he had a great step by step conversion complete with photos etc.

Here's another parts view of what's required for full flow.
The thin gaskets for top and bottom of the canister should be available from Cat.
Best bet is to probably obtain a complete used assembly. Same unit used on D2, 4, 6, 7, 8, 9, loaders and graders plus industrial engines of that era.
 

Thanks everyone, I think I have found someone parting out a D4, will give that a shot!

How bad is the old bypass oil filter system by the way, compared to the full flow?

Also, how important is the oil cooler? mine was bypassed at the oil filter, perhaps it had a hole in it?

The old by-pass system was as good as they could do at the time, before further development of filter media but as it states it bypassed a portion of the flow without filtration.
By-passing the oil cooler is pretty common and development of lubricants eliminated the cooler requirement. Late model U D4's dropped the oil cooler completely and went to full width radiator cores.

I have a complete full flow assembly available.
pm if interested.

Thanks, I have found someone locally in Australia who is parting out their 7U,
will be getting a whole bunch of parts from them including the full-flow filter.

Cheers!
 

we got all the filter and all the seals from hastings deering simple phone call when we last did a oil change.

if you have part number they are quite helpful.

copper washers are still readily available from any industrial or auto parts supplier. NOTE they can also be reconditioned using 600 wetndry a little kerosene and a piece of plate glass to dress them flat then re-anneal by heating to annealing temp with a torch and quenching in water not worth it for the price of a couple of washers.