[Axel Breaker Earl]

Probably the O-ring at the back of the water pump, where the metal coolant pipe connects to it.

 

[Axel Breaker Earl]

The chain tensioner adjustment cover gasket is Mazda part number:

G60110512A

You can just make one from some Felpro gasket sheet material and it will work fine.......I have done this several times. Use a small amount of Ultra Grey RTV silicone on each side of the gasket, and no leaks.

Here is the gasket material that I use.....

 

[Axel Breaker Earl]

Yes. On a G6 engine (B2600i Truck), the Oil Pump is sold with the whole front timing chain cover also......so not the cheapest. When rebuilding these G6 engines though, I always buy a new one.

 

[Axel Breaker Earl]

If you don't have a coolant leak where the steel coolant pipe is inserted into the rear of the cast aluminum part (that your lower radiator hose connects to) that I circled in my picture on post #3, then just save that O-ring......don't install it now.

Here is a image that shows the parts breakdown diagram from one of the online Mazda dealerships.....the O-ring is part number 15-287 in the diagram below.....