Not sure. But I just replaced the priming bulb on my Stepfather's Echo after 20 years. According to the shop they may have 3 or so carbs they use on one model. But, he just gave me a generic Echo primer bulb. You may want to try a small engine repair shop if no one links you to aftermarket ones.
These are clear , plastic things . The rubber one on my mower's been on there forever also , but the 2-stroke ones are just terrible.
The thought of some plastic conditioner is worth a shot, or maybe opening up the parts drawer and finding one in a different material.