Here is a trick. Use the black RTV Gasket Maker to assemble.
No leaks
To get it apart: spray brake parts cleaner around all the RTV sealed areas. Keep it wet with brake parts cleaner for 1/2 hour or longer as you see fit.
The Brake Parts Cleaner breaks down the RTV and it easily comes apart. Whether it be valve covers, oil pan, intake manifold, fuel pump, water pump it's all the same.
No leaks, proper prep, no oil films, then use RTV Black.
☆☆☆☆☆