Yes there are cylinders in drum brakes, usually 2 in each front brake and 1 or 2 per rear, which can leak with age / wear. If any one is leaking it will also mean the brake linings will be contaminated / wetted by the fluid which will seriously affect the braking efficiency / balance and they should be replaced as well, also the affected drum will need to be cleaned with a suitable solvent. Any leaking cylinder will probably mean the rest of them are coming to the end of their lives. As good brakes are important, if you are not sure what to do to fix them it would be best to get a good mechanic or brake specialist to check and advise.

Personally I would not attempt to repair / reseal leaking cylinders but would replace them with new ones.

Yes there is a small slave cylinder in all drum brakes. You can usually buy a seal kit to repair the cylinder. But it's easier and more certain to replace the cylinder. If you DIY buy a 'one man' brake bleeding kit as this will make the job much easier. And place a small piece of plastic over the master cylinder reservoir and screw the cap back on before you start. This minimises fluid loss during the cylinder removal.

A wheel cylinder is not a slave cylinder. The reason brake fluid is leaking is the wheel cylinder is scored because someone has never changed the brake fluid.

Yes drum brake systems have cylinders that hold/control the brake fluid and they can get worn or dirty and start leaking.

A drum brake has a "wheel cylinder". That's the name of the part you are asking about. It could leak.

Yes, there is a "slave" cylinder and they will leak when they get old enough. Remove the wheel and brake drum and it will be at the top, behind the drum.

You should replace or rebuild BOTH wheel cylinders, not just one of them, then flush out the old fluid and bleed air out of the brake lines and cylinders.

Yes, there is a wheel cylinder in drum BRAKES. They can wear out and leak THE brakes fluid. They are easily replaced or if you know how, they can be rebuilt.

Yes.