That pic does not look like a RC12YC. It is a 5\8" diameter, that is a 3\4" plug. A RN12YC is the large plug. I buy in sets of 8 from Amazon and never had a bad one. $2-3 each.
Unbolting the engine is easy. 4 bolts then just slide the engine back. No need to disconnect anything. When reinstalling the bolts.\, you can usually see where the engine sat and the hole line up easy. If the pulleys don't fall off, this is the method I use.