Generally, the cost of servicing a 5 is more or less near to the cost of a new watch (unless you have some sort of rare / collectible model).
I’ve owned many over the years, they are lovely watches and generally long-lasting / fuss-free but it isn’t economical to service the mechanism, and replacing it with a new mechanism is always the preferred option.
I did get a local watchmaker to replace / regulate the movement on a particularly cherished one (21st birthday present) but including a bracelet polish that repair was over £100. You can pick up a brand new 5 for less than £100 on Amazon and even cheaper than that if you shop around.