an old pal of mine vs my old pal

[kompstar]

1. He's an old pal of mine.
2. He's my old pal.

Are the sentences above correct? If 'yes' do they mean the same?

[teechar]

Yes and yes.

[kompstar]

Is there any difference in use between 1 and 2? Are these expressions used interchangeably?

[teechar]

That depends on the context.

[Rover_KE]

#2 could mean he's my only old pal.