Did I miss the part where you check the look of the spark plug? What color, wet or dry? It sounds like a crank seal, is the trans oil level dropping at all? If the exhaust is that clogged it could be because of a crank seal or using incorrect oil for a period of time. What kind of oil are you putting in the injector tank? Describe what the motor is doing when it feels as though it is "seizing". Nice looking 100, hope you get her going.
1993 XR650L; 14T CS, Dave's carb mod, Modified stk muffler, Airbox Mod, Battery relocation, Bar risers, Uni filter, No passenger pegs(to make it super lite), Blue powerband.