The FS45 is a good trimmer if properly maintained but as you suggested, the cost of a tune up might be too close to the price of a new one to make it worthwhile. The SRM210, although a smaller engine, still has decent power. I am very satisfied with my GT2000 which has an older version of the 210's engine.
The line will last longer if you allow the tip to do the cutting. Move in just close enough to the obstacle to clear the grass, don't try to force the issue by crowding the head.

well before you go out and plunk down a few hundred on a new trimmer, replace the fuel filter and put in so good gas. Also inspect the air filter. Check the condition of the fuel lines. They could be cracked. Most stores will sell you a fuel filter and a few feet of fuel line for less than $15. If that doesn't help, take the carb apart and clean it with carb cleaner. Most of the time if you take the side covers off the carb and spray the inside of the carb with carb cleaner you can solve your problem and still reuse the gaskets. I think repairs will be much cheaper than a new trimmer

Try the suggestion of starting. If you give up, maybe should consider buying the same FS45 and keep the old one for spare parts. Use Stabil to keep gas good longer in the future.

If you use the Stihl 2 cycle oil I believe it already has stabilizer in it. It is all I have ever used and have had no issues whatsoever.

"If you use the Stihl 2 cycle oil I believe it already has stabilizer in it. It is all I have ever used and have had no issues whatsoever."

Same here. Of course now that I said that...

Stihl Oil PR release

The question often raised regarding stabilizers in oil is how much and how effective is it. If you are supposed to add 1oz (30ml)/2.5 gal (9463.5ml), that would be 12ml/gallon. Since a 50:1 fuel oil ratio means that you add 2.6oz (76.9ml) of oil to each gallon. If 12ml of that 76.9ml is stabilizer, that gives you a ~58:1 fuel/oil ratio. I just don't think they put that much stabilizer in their oil. I think they put some but not enough for long term storage.

I have used Stihl Oil in the past and was very happy with it. My volumes went up enough that I started using a more specialized oil that I can get by the gallon for less than what the Stihl single . I don't think the oil I use has stabilizers. It is not an issue for because I add stabilizers if I know the fuel is going to sit for awhile. I use stabilizers once or twice a year.

I don't think you can look at it as volume. Because you have to take into consideration of the concentration. If Stabil is 10% solution mix in petrol base, then you really talking about 1/10 oz for one gallon.

But anyway, I agree with the principle you have that put in your own stabilizer. I use Amsoil that have no stabilizer, so it is a must for me to add Stabil. With the alcohol in gas, I use the Blue Stabil that keep gas good for supposingly one year. And if adding extra, can last longer.

I agree about the concentrations. I just wonder if there is something more concentrated. In all the discussions I have read no one has mentioned that there is a higher concentration type stabilizer.

Original question was not about oil?

My logic is if it is more contrated, it can be hard to measure such a small amount.....eg. 1/10 oz portion.

OK, I'll drop the Stabil issue!!!