Should i buy a Peterbilt 387 2004 with MBN 475CAT (small coolant leak ) for 10000$ ?

Hello , a friend of mine have a Peterbilt 387 For Sale , the truck have a MBN 475 CAT inside / 13 sp , the engine has 1k miles and was rebuild by CAT at 500.0000 miles because of a bad liner / coolant leak .
The problem is that now the truck have again some coolant leak , nothing really big , around 1 gallon by month , oil samples are coolant free and very clean , my friend say that at each oil change at 15000k miles it takes no oil and the level is still the same as when it was changed .
All the 10 tires on the truck need to be changed as well .
He wants 10000$ firm ,other than that the truck look good and drives well.
I have a Volvo 770 / Cummins ISX / 13sp right now with 1.1 miles which needs to be overhauled and it will cost me some 21000$ with everything that i want to put inside.
So i was thinking why not sell the Volvo for some 9K , then buy the 387 for 10k , repair the leak and transform that MBN in 6NZ .
What you guys think ,also i always wanted to have a Can C15 6NZ under the hood , life is short , i am already 42 old , also i am 6.5 tall and i am very comfortable in the Pete 387 seat.
Also i just read about mbn liner protrusion problems that can cause a cracked head and/or blown head-gasket , can this be my coolant leak , are the shops aware in how to set this liner protrusion to the right specs so it will not happen in the future ?
What is the total money needed to be invested here to repair and convert to 6NZ ?
Is this worth it ?
What that coolant leak can be ?
Any other common problems with MBN series ?
Thx for your time.

 

Hello guys and thank you , the engine has 1.000.000 miles and was rebuild by CAT at 500000 miles . No warranty on engine . Also where to find such truck in good condition with 12-14 k , the same truck in truckpapper in good condition is around 22k.