Completing a 100hr on our flight school Seneca II and the gear goes through this disturbing bounce / shake dance during normal extension. At 1st I thought it was just the nose gear but after isolating the actuator the mains then do a similar thing. Power pack fluid level was unchanged from the last 100hr ie full to the top of the filler port. Emergency extension is all smooth and perfectly normal. Only thought I have is to replace the power pack although I'm not sure if that is the problem since retraction works just fine. Anyone seen this before or have suggestions before I make a $2k hipshot?