Looks like grease that was thrown out of the slip yoke of the driveshaft. It was probably over greased and it’s just working it’s way out. That ring on the back of the yoke where the splined shaft goes in usually has a seal behind it, might see if it’s loose.
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Brian & Jeannie
2018.5 Seneca 37RB with to many mods to list
2015 Jeep JKU Rubicon
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