Every Grasshopper I've owned (if replacement bodies count along with straight repairs, then I'm well over 12) has slowly reached a state of restricted draw. Units that have gone for repair come back great, drawing "like new".
The only advice I've been given by HL is to swab out the chamber with iso , then blow compressed air through the intake holes (they even warn, "your breath alone is not enough." or some such thing.
Occasionally this has worked, though never getting back to original this way...and I have at times been very thorough with it because I really want the piece to work like it's been capable of working in the past. I currently have a Ti that just will not clear up -blowing as directed, but eventually through all orifices while running at temp 5. (the air movement will override auto shut off!)
Back in the day I would look forward to the next fail because, well, at least it would come back with improved draw.
I pulled that Ti out today and it was a big disappointment compared to my current friend, the Vleaf Go. At <60 bucks the Go has some qualities that are a very pleasant change from marriage to Grasshopper. No screwing! for one. (Now that sounds a little weird...)
I know a lot of owners have gotten vg mileage from their Grasshopper, but that has not been my experience. Really, it's purchasing multiples that has kept me on the ride. Now that warranty work is almost non-existent, my ride may be coming to an end.