I just got back from a 2500 mile trip and noticed a wet spot under the trans. It seems to leak on these long trips ( it did the same thing last year). Around town, not a drop. What gives?

While checking the oil this morning, I noticed while the engine was running that sp wire #5 was vibrating. I reached down and held the boot and could feel a rythmic, light knocking. The same thing with #6, but less. None of the other cylinders felt this way. I just turned over 182500 on this trip. Any ideas?
Thank you!

 

On a long trip the trans may be building up excess pressure because you may be making large changes in elevation. Check the trans vent ( I think its under the shifter boot), it may be clogged. Same situation with the xfer case.