No I didn't know about the oil cap test. I run my vehicles until the bodies are gone or the cost to repair them mechanically is not a wise investment. I'm looking for a 7.3 engine so that I don't have to spend thousands of dollars bullet proofing a 6.0, like I'm currently doing for my 2005 F250 CrewCab truck that I am building. I'm also tired of paying the local Chevy dealer insane money to fix my 2008 Escalade ESV Platinum vehicle that is so f*#*#*# complicated that I will never ever buy another one if I get my way, but my wife may disagree. LOL
at 250k I would prepare for the worst and lets just say from my experience at those miles I would expect the following to be need to be done if it hasn't recently.
all 8 glow plugs, both under the valve cover harnesses- aprox: $250 USE OEM you don't want a cheap glow plug tip melting off or stripping...
Hpop lines-$140 from cncfab llc
fuel bowl revuild kit like $68
IPR/ICP sensors plus wire harness ends $450
oil cooler kit like $70
at250k plus its really 50/50 on injector but assume motorcraft stock remans maybe $1k-1500 plus 8 injector o ring kits maybe $60-70 USE OEM.... autozone, oriley ones will make you regret when they fail couple hundred miles down the road... use OEM for all the parts above you can research and see the nightmare generic brand IPRs and UVCH caused powerstroke owners... total like : 2500$ assuming the worst etc. Also the transmissions being a 4r100 arnt known to last much more than 150k so at 250k or 350k+ assume like $2500 for rord reman or a bit more for a sam wyse stage 1 or bts stage 1.
still was cheaper than my previous 6.0ls but at 20 yrs old they just have more thins that will need replaced sooner than later and again stick with oem parts/ o rings or you'll end up doing many thins twice costing more $$ and time in the end vs maybe 20% more upfront etc. This is all generally speaking from prices I pay at riffraff diesel and cncfab llc. every truck will be different and excursions are not much different except the PATS security system
within the first year I had to do glow plugs, uvchs, then 2 years later ICP, and IPR, and hpop lines, then fuel bowl reseal but my truck is now 100% leak free