That depends. How serious a hole are we talking about here? If they are just small/tiny holes then they can be sealed up. If they are larger or too numerous to make sealing them worth the time/money investment, you might just replace them.
If there is leaks at the corners or where sections join yes you can seal them. You need to clean the area real well, lightly sand the surface, be sure not to cut yourself and use a good quality sealant that is used for metal.
If there are holes just in the gutter itself, this is a sign that the gutter metal is worn out and even if you seal these holes, more will appear as the gutter is failing. Your best bet if that happens is to replace them.
That depends. How serious a hole are we talking about here? If they are just small/tiny holes then they can be sealed up. If they are larger or too numerous to make sealing them worth the time/money investment, you might just replace them.
If there are holes just in the gutter itself, this is a sign that the gutter metal is worn out and even if you seal these holes, more will appear as the gutter is failing. Your best bet if that happens is to replace them.