Electrolytic capacitors are pretty much made from paper, foil and electrolyte. With time the electrolyte can evaporate and/or leak. This can affect their operating parameters and it is best to replace them.
On the 2018 the main capacitors to replace are on the Control Room card and on the I/O card.
Control Room Card
I/O Room Card
Below is the bill of materials for both boards.
Our favorite supplier of components is Mouser, so we are providing their part numbers as well.