Eaton 18spd Intermittent Problem

[MSPOIRIER]

Good Evening,

I have been working on this one for a couple months now systematically going through checks and repairs but so for no real progress. I have an 09 International 5600 with an Eaton 18spd (RTLO18918B) that has the quick grind coming out of low range to high. Anyone who has been around would say the synchro in the Aux section. My hang up here (and my local Navistar Service advisor Agrees)has been it only happens a couple times a day if that. I have gone through all Eaton Procedures including disconnecting and blowing out lines, replacing filter/regulator, doing system checks with test gauge, checking fluid levels and replacing air dryer filters a couple times. The lube cooler is air to oil so I don't suspect coolant contaminating the friction on the synchro. The thing that has me hesitant to open up the aux section (besides the truck working everyday) is when the truck is in Neutral running or not it does not always shift in. You can hear the normal burst of air but some times it does not "Clunk" in. Sometimes it wont clunk a couple times in a row. When this is happening I am still showing and holding 65psi on the gauge at the range cylinder. I am going to order the cylinder o-ring kit from the dealer tomorrow and try that as my last effort but I am interested to see if there is any new insight from members of the site to see if there is anything I can try that I have not thought of. This problem never occurs going from high to low and the truck only has 134k miles on it. Also if this is relevant being a higher HP truck with very low gears I do tend to shift across the Range without using the splitter. (4H-5H or 4L-5L) I don't see what that would matter but I'm trying to think of everything. Thank you for reading this far!

Sam