82 300D new project -wont start...

Just got this car two days ago Black 82 300D turbo diesel. straight body, clean interior, new tires, was running two weeks ago at 347,000 miles.
PO knows squat except it wont start...
For 500 bucks I figure its worth the gamble...

Day 1 trailer home, look it over, battery worn down from po and all the lookers tryin to start. pull fairly new batt and charge...

Day 2 hook up batt showing 12 volts, check grounds, gp relay reads 9.? volts, air filter clean, oil dirty, 1/2 tank diesel, see new fuel filters...give it a whirl.
Motor turns over, but slowly...with good batt I think probably a week or worn out starter/solenoid ?????

Day 3 was going to check wiring and maybe cleanup starter(quite a bit of oil n gunk down under), maybe go ahead and pull starter...
But two days worth of storms just blew in, so here i be...
My first MB, first diesel, so i could use any advice yall might toss my way.
Theres other issues i see need tending to, and probly more to come, but obviously i gotta get this thing turnin over right to tell much else?

Thanks guys I've learned a bunch just searchin the threads!!!