Hello everyone,
I'am new here and i'am new with the mazda's

Just bought Mazda 6 2011 2.2 Diesel with 163hp and have couple of questions about it.
I have read a lot of opinions about that 2.2 diesel engines before buy one.
Mileage shows now: 159000 km. +- real.
What i have done now: Oil change, oil filter, fuel filter change, air filter change, cabin filter change.
Also checked the engine chain degree it is 8.07. What i know it's pretty good? Change needed if degree is 10.45?
I don't change injector seals yet. How to inspect that injector seals are bad? Oil is bright not dark. After oil change i drove about 300-400 km and oil is still bright.
What i really want is to prevent the damage to this engine and want opinions what i should do more for safe using this car? I think there is two main problems with this engine: chain streching problem and injector seals who leaking and diesel gets in the engine oil. Am i right?
In the internet i have found that a lot of have problem with crankshaft? What cause the crankshaft cracks?
Waiting for others reply! Thanks!