Shops blow out the tubing with compressed air. Their air compressors are usually much more heavy-duty than the homeowner type compressors and they have more fittings that can help blow it out. If you have a compressor, you could try it yourself first.
I'd be surprised if the seal itself is bad at 6 years old. However, if the car is always in the sun, that could degrade the seal. I've always had good luck with seals and weatherstripping when treated with 303 aerospace protectant. I also use it on my dash & tire sidewalls to prevent checking. Boating places are ahead of auto places on this and you can find it at West Marine or almost any canoe & kayak shop. I use it on weatherstripping, seals and gaskets 3 to 4 times/year. We just sold a 16 year old subaru (frameless windows) that was always treated with 303 Protectant - and the weatherstripping was like new, soft and pliable.