agree, pull glowplugs, fill cylinder with 50/50 ATF/acetone, wait 2 day, test if wrench turns it a bit, add more ATF/ace, wait another day. repeat process until engine turns over with wrench. Do NOT use starter to turn over ! Use wrench to test move crank round maybe 10-15 degrees .When you use excessive force, you'l destroy rings and things. Do not try to START the engine until you clean the oil out of the cylinders !
My first D-14 was 'stuck' , has sat 25 years. It took 2 weeks of this 'oil fill-test turn-next day' routine. Once it was free, gently turned crank BOTH ways, several times, walked away. NEXT day, removed oil in cylinders,spun crank with starter..seemed smooth,fresh gas, plugs, choke, she fired up ran smooth, fumigated the garaged.... been running fine for past 23 years.
You MIGHT get lucky, but have to have a lot of PATIENCE.....