Need advice on '99 century

Ok guys,I own '99 century,12.7 detroit for 1 year now.I bought it of the friend and payed 7300$ and at the time it had 1 023 00 miles on it.Now,after 1 year and 100 00 miles,I need advice what to do.It wasn't really a money pit,in one year i replaced head,radiator,air dryer,air compressor,oil cooler,injector cups...rest is oil changes and small things like two sensors,some valves,air bags.I did oil change couple days ago,and mechanics found few things that needs to be fixed:

1.I have oil in coolant,but i have it since i replaced head,and mechanic who did it says it is old oil that was in the sistem before head was replaced,so i dont't know,maybe they didn't flushed it properly,or maybe its new oil?Im driving truck like that last 5 months.I can see inside the coolant tank there is old oil glued to the wall of the tank and they say it can't be washed out??!Maybe I should replace the tank and let my new mechanic do proper flush and see what's going on then.

2.I have oil leak in front differential

3.Front bushings are worn out

4.Coolant pipe from radiator to water pump is rust and leaking coolant little bit

Truck has been good,considering what I paid for it.Im trying to fix on time what ever needs to be fixed,if money allows.Im getting 7.5 mpg most of time,but Im avoiding heavy loads,don't like to torture my black mamba

So,I was thinking,should i go for an overhaul and fix all this,or should I keep driving it till spring when registration expires,sell it and put my ##### into payments for used 50K truck?

 

Yes,100k,forgot one 0 Yea,you never know.My friend drove 08 cascadia,company truck,and had to do 2 overhauls in two years???I changed mechanic few months ago,this one is very serious shop,very happy with them so far,just still don't know what to do,plus business is slow at the moment,winter is coming it's gonna be even worse.Need to think hard on this one,thats why Im asking for advice from more experienced people here.

 

Thank you guys,really appreciate your help.I'll try to make some more money before christmas,then will take few days off and leave truck in the shop and fix what needs to be fixed and to test things needs to be tested.I don't like payments,thats why Im leaning towards the overhaul,if it's needed at all.

 

I don't know.Truck was owned by some mechanic guy who did some regional run,auto parts industry,then it was owned by guy who drove for Triple Crown,he sold it to my friend,my friend sold it to me.Truck is now black,but i think it was involved in some minor accident and had to be painted,I think it was blue,so it might be ex Werner truck