In July, I had the dealer repair a leaky transmission oil pan gasket. I supplied my own OEM part (BW6019835), but the dealer didn't install it, claiming that they replaced the old gasket with RTV silicone seal.

Is this normal or acceptable? It bothers me a bit that they directly ignored the Mazda service manual.

(I now have an ATF leak, which may or may not be related this repair. I'm very concerned that the dealer messed something up.)

 

They have a shop manual to take the guesswork out of the work. If the shop manual specifies a gasket, you have pretty good grounds for an investigation as to why it wasn't used and how the dealer would like to help you.

That said, it's pretty common even from the factory to use silicone. Toyota uses nothing but. The catch is, the silicone needs to be compatible with the fluid it's sealing. If say ATF were to break down the particular sealant your dealer used, that would be bad.