R&R Hydraulic fluids - any problem with air pockets?

I've been enjoying/working my new D2 4U and it has been working well. Thanks to many here I'm familiar now with dozing and overall operation of the machine. What a brilliant piece of American engineering especially if you remember this was designed around 1950. I'm so glad I didn't waste time with any Chinese junk.
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After replacing the transmission oil because of water now I see we have plenty o'water in the main blade hydraulics. So, I've got four gallons of replacement fluid ready but now sure how to go about changing it out. I've got seepage of white/gray looking fluid at the cylinder seals so I know the entire system is wet. To drain all the lines I'll just loosen or remove the line connection(s) and let gravity do the rest. I'll be sure to drain all segments but that's where my question starts. Once I reconnect the system I'll fill the main reservoir and planned to let the air out of the lines going to the two blade arm cylinders at the lowest point until fluid comes out instead. However it doesn't appear that I'll be able to get all air out of all segments unless running the system under pressure.

Question: Will the seals allow the air but not new hydraulic fluid out to purge all the air? Do I need to worry about bleeding the system more than described above? I'll just dive in and begin unhooking all the lines if that's okay ( good time to replace any worn lines/connections). I just don't want to take it apart and not be able to get back together properly. thanks in advance.

You may be able to get rid of more of the contaminated oil by parking the tractor with the blade up and so it can go down as far as possible (park on a hump or block?) and then with the engine stopped, lower the blade and then drain the resevoir and loosen the lines if you want. The hydraulic system should purge the air quite easily on it's own once you crank it up after refilling as full as possible. Just cycle the cylinders through full strokes several times and then recheck your fluid level and bring it back to the proper level.

Does your tractor have a CAT hydraulic control unit on it? Have you got a new filter? If it's really bad you may want to take the front off the hydraulic unit and wash out any sludge in there instead of possibly having to change the oil again as it cleans up the system. Very common to have a seal on the control shaft that's letting the water get in. I think you can stack a couple in there to help stop it since the shaft is probably pitted or grooved a bit just where the seal rides, or put on a speedy sleeve to cover the worn area.

ccjersey is right on about that seal on the control shaft. I had to remove the front cover and pull the shaft to put a speedy sleeve and new seals to keep the water out. Just for the heck of it when I got done I put some grease on top of the seal before I put the control arm and washer back on. I thought it would be better than letting dirt pack back in there and ruin the seal....again.
The guys here have been exceptionally good to me with the information on repairs to my D2.
Have a good day..........Bill