Old king gets sticky substance - perhaps resin - on the inside (5,1)

'resin on the inside' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.

'old king gets sticky substance' is the wordplay.
I cannot really understand how this works, but
'king' could be 'james' (I've seen this before) and 'james' is found within the answer.
'substance' could be 'i' (I is an example) and 'i' is found within the answer.
This accounts for all the letters.
This explanation may well be incorrect...

'perhaps' is the link.

Can you help me to learn more?