My new to me Maritime HG sounded so good and played so badly I had to look into what was causing the issue. The guitar sounds wonderful but the intonation at the G, D , A and Low E strings was slightly high when pressing the 12th fret. Playability was pretty poor too. The action height at the 12th fret was not too bad. The action at the 1st fret was terrible. Somewhere high of .030".
I traced both issues to the Nut. Firstly the nut was not properly installed, it was slightly tilted ie: not sitting squarely against the fret board. I ordered a replacement nut Tusk # PQ-1801-00. Once the strings were out of the way the original nut popped off with a slight tap. What I found was a lot of adhesive under the nut showing it was not carefully installed and sitting crooked in its place. I cleaned the area where the nut seats carefully and placed the new nut there and then put the E strings back on and measured the clearance at the 1st fret. Some sanding of material from the bottom of the nut gave me the 1st fret action/clearance I was looking for. I'm using the StewMac suggested setting of .023 Low E and .013 Hi E No fret buzzing and greatly improved playability now. The nut being crooked/tilted appears to be the primary reason for the intonation issue, I was just cocked enough to shorten the string length and cause the minor sharpness when being played at the 12th fret.
I most likely could have used the original nut it cleaned up nicely but since I had a new one on hand I used that.
Bottom line if your Seagull has similar issues look carefully at the nut.