Welcome to the Celica Hobby Forums,
Sounds like to me that you may have a break in the Timing chain cover seal, or the Crankshaft (Front Main) Seal located right behind the harmonic balancer/crankshaft pulley.
However it is possible you could have a leak from the valve cover gasket and its traveling down.
As seeing at the timing cover is on of the more larger seals and the way it sits vertically instead of horizontally and the change when changing the timing chain tensioner leads me to believe that is the cause on a sight unseen basis. I know that its super tight but if you could get some images of video of the leak that would greatly help in trying to figure out where this leak is coming from.
If you do attempt to do the timing chain cover seal you may as well as replace the valve cover gasket and the "front main seal" as you will need to remove all of them to do the timing chain cover seal. However, that is highly labor intensive and will leave the vehicle out of commission for a while.
Yeah, if you could get images or a video, we can try to pinpoint and explain exactly what needs to be done to fix the leak. I am giving you information off the top of my head from when I had to do a engine swap and I tore down the blown engine. Which may not be 100% accurate or the cause of your leak.
