My biggest source of an Oil leak turned out to be the Valve Cover Gasket. And, I suppose if there was a problem with the Valve Cover Gasket and you have high Crancase Pressure caused by blow by it would even leak more.

If you have not done a Valve Adjustment yet it is possible the Clearances are tight enought that it is holding some Valves slightly open. This would result in a compression loss.

I found out many months ago that my Volvo Diesel that had sat for a year (until I got around to changing the leaking IP Drive Seal) and also partly due to my Thermostat sticking open (creating a low operating temp) had developed a case of sticky rings (this would also effect the compression).

I removed the Golw plugs and used a Meat Injector Syringe with some Vacuum Hose on it to inject about 1/4 cup of Marvel Mystrey Oil into the Cylinders in hopes of disolving some Carbon or otherwise unsticking my Piston Rings.
I let the Car sit for 4 days and repeated the above and let the Car sit for 2 more days.

With the Glow Plugs still out I cranked the Engine over to blow out any excess Oil and prevent a Hydraulic Lock.

Put the Glow Plugs back in and took the Car for a 1 hour drive on the Freeway. (I also had changed the Thermostat.)
The Freeway drive only brought some improvement but over the next week it gradually got better.

I mention the above as it could be possible you low compression is due to stuck compression rings. Also the Marvel Mystrey Oil does not cost much. But, you do need to be able to pull all of your Glow plugs out or be willing to pull the Injectors and replace the Heat Shields.

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84 300D, 82 Volvo 244Gl Diesel