Need channel balances for wood doublehung tilt windows

Thanks for posting. It's possible this is a Series 751 Channel Balance, with a ribbed metal channel. Removing the balance is the only way to know for sure. Unfortunately it is impossible to replace these types of balances without removing the jamb track. The video below shows how to do this; but if you are uncertain, hiring a professional would be best. I don't know of any handypersons in your area specifically, though a cursory glance online tells me this business here has a good reputation. If you can get those balances removed for us to inspect, we'll do our best to help. Many thanks. 

I see what you mean. In a lot of cases these jamb liners are just pressure fit, meaning the presence of the sash keeps them in place. Removal of the sash should theoretically allow you to just pull the jamb out by hand, but you are right to be worried about how brittle the vinyl has become with age. It's a major concern.

One trick you could try is making a soapy water mix and spraying it on the window sill right under the jamb liner. This will act as a clean, mess-free lubricant that will hopefully help convince the jamb liner to come out. It's not a guarantee but it's a handy trick that I've used myself to great success. 

Sounds good! Please feel free to reach out if you had any other questions.