When cooking fatty things such as pork shoulders, etc. grease atomizes and goes EVERYWHERE! It's just the nature of the beast. If the grease works its way in between the lid and body, then it starts to wick it. The only thing to do is a thorough cleaning and get as much of the grease out of those layers as possible.
After a thorough cleaning, I don't see why you couldn't seal the inside of the seam with some high temp sealer if you wanted. I've used it in other grills/smokers without issue.
I got to thinking about this (too much time on my hands! :-). I wondered why I do not see the same issue with my Weber Summit gasser. I have certainly have grilled many a fatty food on it over the last 10 years and it has never had this kind of issue. Design wise, it does not have a vertical seam on the sides or rear of the cooking chamber. It also does not have rear vents, which on the MAK I imagine are integral to the smoke flow the MAK needs by its design. The Weber does have two large openings on either side for the rotisserie.
The hood/door is similar to the MAK, that is it opens over/around the rear, fixed section of the cooking chamber. However, the sides of the fixed section are higher and extend much closer to the front.
Nothing profound here, but I do think MAK might consider a design change for the future that includes some sort of grease splash guard for the vertical seams and vents. Obviously it will not eliminate splatter, but could significantly reduce the leaks from these unexpected places. Just my 2 cents.