Do you mean the front cover? MazdaTrix carries a lot of small parts. Check your oil injection lines and pump for leaks, they run along that side. I had a leak there before. If you don't know where they're at download the FSM (Service Manual) from
http://foxed.ca/foxed/index.php?page=rx7manual
The manual will help in trying to track down the leak and many other things. A little hard to diagnose without seeing it.