Removal of the filler plug followed by the drain plug will give you the washer size(s) if any.

Wouldn’t recommend reusing a sealing washer.

IMHO any off-the-shelf annealed copper washer of suitable size would do.

Check for leaks after a short run.

Chris

2015 Plus 4 Silverlake Blue
(2014 3.7 Roadster Crystal Blue)
(2012 4/4 Sport Black)