E key wearing is common, as E is the most used letter in typing. You will need to clean the mechanism, easiest is to use some illuminating kerosene and a bottle brush, and scrub the inside and bottom of the unit, then rinse with clean kerosene, then apply some light oil to all the pivots again to lubricate them after the kerosene has dripped out with all the gunk in it. That will solve most of the sticky keys, and will make the rest easier to operate.
To clean the platen you will need rubber cleaner, or use methylated spirits or IPA to wipe most of the residue off. Note rubber cleaner is death to paint. To get some you need to find a local offset printer supplier and order some, or ask nicely at a local small offset printer if they will sell or give you a nearly empty can. To clean the keys the printer will have Blankrola, which is used to clean ink off, and which will work there. that is also good to keep off paint, but it is water soluble.