2002 Toyota Camry, 240K (Hwy miles mainly), 4 cyl

Hi, we just had a rebuilt engine put in after the original engine siezed up at 232K. Couple of minor oil leaks repaired since. Took car in for oil change, nxt day smkng and leakingfluid. Took it back to oild change place, thinking it was oil. They found that it was transmission fluid and that 'clip' attaching drive shaft to cv joint had come undone and fluid was leaking from there. They tapped it back into place and reattached clip. Put in 3 qts of transmisison fluid. No leaks in three days but car is still not registering fluid on transmission fluid dipstick. Inside of front psgnr tire has grease which I assume is from whatever it was that was open (cv boot?)That had to be tapped back into place. Also see hole when wheel is turned hard right on the boot opposite the one connected to the wheel. We'lll be taking it back to our mechanic but need some help knowing what we're talking about. The most troubling part is that we took car back when we heard a 'chain clanking' sound coming from under the car about three week ago. Mechanic said it was honeycomb structure w/in catalytic converter, no crisis. But after guy tapped the clip back into place that noise is gone. Can you help us make sense of all of this? :( What might be causing the leak, is our cv joint likely needing replacement now too, why doesnt the fluid register on the dipstick? Please help!