Ok, you say the tranny slips, when it does this, do the engine RPM's go up? Is it making any noises? Do you have a check engine light on? You say oil shot up the dipstick, were you trying to check the oil with the engine running? How much oil is in it, and how long has it been since it was changed? The only thing that can cause a manual transmission to slip is a bad clutch/pressure plate assembly, or bad slave cylinder. Did you do the clutch replacement? If you did the work, did you replace the slave cylinder as well? If you had the clutch job done by a shop, you need to take it back to them, and have them look at it. As far as the oil leak goes, are you talking about the gasket at the top (cam/rocker cover), or down lower, the actual head gasket? I really could use some more info, and a pic of the oil leak would help.
