Do you think it's worth replacing them since it is so old?
Depends on what it will cost to repair, how good of shape the unit is in and how happy you are with it.

I would open it up find out what is causing the no heat problem.
Then I would check the unit over. Check the belt, rear rollers, front supports, idler wheel, drum seals etc. for wear and bearing slop.
You may as well do a basic overhaul while you have it open.
This also will give you a total cost of repair.

If you do not own a meter, I would suggest you purchase a one. You can get a decent digital multimeter for under $20.00. You do not need fancy though it is nice if the leads are a couple feet long.
If it saves ordering one unnecessary part it has paid for itself and you end up owning a useful tool.
Most places will not let you return electrical parts so if you order it, you own it.
A couple things to watch when measuring ohms and continuity
1. Always remove power from the machine otherwise you could blow your meter.
2. Always disconnect at least one side of any device you are checking. This eliminates the possibility of measuring an alternate/parallel circuit path.
3. When checking for closed contacts and continuity use the lowest scale (Usually 200 ohms). Then try higher scales. This scale is 0 to 200 ohms so if the device you are measuring is 300 ohms this scale would show an open circuit which it is not, you are just measuring outside the scale's dynamic range.

There is a good STICKY at the start of this forum about it's use.