LB7s most commonly lose coolant through pushed cups most of the time. I had one truck in here a while back where it was so bad it would hydrolock the engine sometimes. Luckily the guilty cylinders were at tdc when this happened.
Like Tom said, If the guy/shop knows what they are doing, they should automatically remove all the cups and reseal them and if any cup(s) are bad, replace them, I usually replace them if the majority of them are bad but not often. when I do these jobs I usually end up doing the headgaksets anyway, as I pull the engines for these types of jobs (only takes me an hour to yank them by myself). When ever I come across a pushed cup(s), I always want to remove the heads to see if there is any cylinder damage/washdown. I had one that bit me in the a$$ because I didn't take the heads off and inspect everything and turns out multiple cylinders had bad rings (learned my lesson there, but I took care of it). Thats just me though.
I mean, you have to tear down the engine most of the way regardless to do injectors on LB7s, I don't see why not go further and have the headgaskets done with studs as an extra insurance policy. when I go through these, every consumable gets replaced, heads get sent off to be checked and cleaned, injectors and pump get sent off for testing (unless I'm changing them.) and Turbo gets taken to my local place (I use Comp turbo) to get inspected and refreshed. If I do see anything wrong with the engine I let my customer know what I found and basically tell them it would be easier an worth the expense to have it refreshed at the machine shop since its already torn down. Its nice that Mahle makes an overhaul kit for these, as most guys can't justify the expensive performance parts for a stock truck, this makes for a great alternative.
and when its all done, everything on the engine is fresh and or refurbished to last many more miles ahead. I have to go this route as I had and still have fleets and hot shot drivers that can't afford to be down. Its expensive up front yes, but defiantly worth the investment in the long run.
The types of jobs I got were mainly redos because the customer didn't like my price to begin with, took it somewhere else, somewhere down the line something went wrong with the job (either the shop cut corners or the customer declined parts and or services, I never know the truth) and they want me to fix it. They basically pay double because I tear everything down and start over, I don't fix other people's mistakes, I get rid of them.
But in the end its entirely up to you what you want to do. Me personally, I would do both injectors and Headgaskets and studs.
But if you did buy your injectors from eBay or just some random place on the web thats not well known and they were very cheap, don't expect them to last. Theres lots of companies selling "low cost" injectors but don't last worth a damn. Most places wont install parts that you bring anyways just because they don't want to be held liable for anything going wrong with them. Or if they do they won't honor any warranties.
