2012 Paccar?

Ask for maintenance records.

For linehaul at this mileage you gonna be due for.......

DPF reman or cleaning

Engine Management sensor cleaning and EGR system flush.

Overhead set probably not a bad idea.

If there is no documentation of these items being completed recently, plan to do them pronto after taking possession.

All of this will be accelerated with high idle time or light load operating conditions. Taking the unit in for chart recorder and regen history review before purchasing would be a smart play.

 

Everything @Goodysnap said is dead on. Trouble with most newer trucks is nobody actually wants to do all the preventive maintenance tasks.
EPA10 MX vs EPA13 MX uses more EGR flow to control NOx emissions. This tends to soot up the air management sensors and devices. If buying from a Paccar dealer, I would suggest you have these items done. Air management service, Venturi tube and sensing tubes cleaned, EGR cooler flush (much quicker with Paccar tool cause quite involved removing it) HC doser cleaned or replaced if not OOP style, DOC and DPF cleaned, decomp tube and DEF doser inspected for DEF buildup, DEF pump filter replaced, and make sure PMCI/ACM/DCU has most up to date software. I would also have them check Cruise/ speed settings and PTO settings making sure it is what you want.
Other things I have had issues with on EPA10 MX engines:

Fuel pipe leaking from unit pumps to injectors. Should have small rubber dampers on them. Any appearance of leak should be addressed.
Fan belt tensioners tend to "twist" down. Don't think they ever come up with true fix, just replace with another one.
Centrifuge oil filters tend to wear out the bearing in the oil module and cap, especially if not running OEM filter. Best to run Paccar filters.
Not an engine issue, but Paccar really pushed Borg Warner/ Kysor fan clutches around those years. 300,000 seemed like the lifespan.
I attached an early MX maintenance recommendations bullentin. Overhead mileage has been lengthened, but probably wouldn't hurt to peak inside. I check it everytime I clean the DPF which we have settled on 240,000 for the EPA10's

 

The Mack will need all of those things done too! We have two 2009 Mack's with the MP7 that we bought when they had about 185,000 on them. Both needed injectors and cups before 250,000 miles. Both have needed EGR coolers and valves replaced, new complete engine harness (PITA). Both have needed fan clutches around 350,000 miles and pricey viscous ones. Put an air compressor on one and CCV module on other which was over $900 in parts. Had to replace a cracked DPF on one Mack, turbo on the other. The service department @ my local Mack dealer doesn't have much good to say about the "red Mack" motors.
All in all, the MX has been better than the MP7 in my fleet. The deepest we have been inside on of our EPA10 MX is an injector. Have two over 800,000 miles and a couple in the high 600,000.
Good friend who works for Penske that is darn good tech has nothing good to say about the Volvo D13. MIL lights are never ending battle along with after treatment issues. He has said the DD13 have done much better in same application.
I guess you need to decide what your maintenance program is and who will be working on it. All emissions engines require more maintenance than pre-emissions engines and the manufacturers haven't been the best in stating realistic intervals and procedures. Other options exist, but they often cause more problems than they fix. You still want to buy a truck?

 

Where I'm leased on to the most popular truck is a Cascadia. Most of us have old trucks that weren't spec'd for this type of work but they hold up. It's my first DD15 and I'm a huge fan. As long as these things aren't idling, I don't consider idling when I'm loading and unloading because I'm using the PTO, all night there's never any trouble. Well besides my truck looking like it's ran the Baja about 90 times in a row.

But if I continue driving I'll sell this truck and buy a glider, if I can. It's not in everyone's budget but it looks like the payment will work out