Hello first time poster, I have a 2004 Ford F-250 6.0 I bought about 2 years ago it needed work guy only wanted $3,500 for it so couldn’t pass it up. After doing tons of research I went through the truck to find all the problems it had (mostly bad injectors) came to find out the black plastic fuel pressure seat was cracked causing low fuel pressure which resulted in 4 injectors killing themselves (injectors came out in 2 pieces when removed for replacement). After searching all over online for a good decent priced injector source I decided on Warren Diesel 155cc with stock nozzles and new spool valves these came with an 18mo warranty. Ordered a set of 8, Installed them tuned the truck with their tune using sct tuner and religiously changed my oil every 5k miles with Rotella T6. About 3 months ago on my way to work I had an injector quit on me with a low circuit code from what I gather this usually means the injector solenoid let go. Called warren diesel and turns out I was 2 months out of warranty and the lady asks what oil I was running and I told her the Rotella T6 that everyone on all the diesel forums swears by for the 6.0 she says actually we found that T6 is to thin of an oil and causes the spool valves to score and scratch and stick and recommend conventional Schafer’s oil. I ordered the replacement injector from them and replaced it doing an oil change at the same time, couldn’t find Schafer’s in my area and Rotella T was on sale so that’s what I went with figured well it’s a conventional oil. Fired truck up ran great again, about 300 miles later an injector on the driver side stops firing this time with a contribution balance code. Called warren diesel again and they said the same speal about the wrong oil and said even the Rotella T was wrong if I couldn’t find Schafer’s to use motorcraft oil. Guess my question out of this long winded post is do you think they are blowing smoke? The way I see it diesel oils with the same weight should all be close to the same? 5w-40 vs 15w-40 conventional or synthetic are all gonna have the same viscosity at operating temps correct?