Detroit 12.7l burning oil and excessive blowby

I have 12.7 60 series with 1.5 mil + that runs decent and has good torque but recently taken on a rank odor like fresh asphalt. It is really pouring exhaust out of tube. It has been using about a gallon of oil every couple thousand miles (weekly). It does have some small leaks, nothing new, but not terrible.
Question; anything I can do to extend its life without major? It did have a new head put on @ 555,000 due to screw on jake coming loose but has been a great runner.

 

Yes I certainly got my money out of it, its just that it still runs decent.

 

No work done on it. I guess keep adding oil until I either fix or replace - would like a newer machine its a 98 9200i.

 

How about Lucas stabilizer, heard that may help?

 

Never heard of adding gear oil, is that i or 2 gallons to the oil change?