Boiler heater element should be pulled on any used espresso machine of unknown usage (History of repair). The Heater element and internal condition of the boiler will give a good indication of the equipment history.
Examine the element carefully. *** DO NOT SOAK IN ACID! ***! This will only enlarge any existing pin holes in casing. Just wipe down and brush up scale with wire brush (wire wheel okay). Keep buffing with light pressure. Enough to shine copper case but not enough to gouge a hole. Check for lines of discoloration as it's probably a crack in the casing. Replace any suspicious elements.
brush electrical lugs of rust for good connection.
Be careful not to damage (Nick) gasket (probably stuck on boiler) and reuse. High Temperature engine gasket sealer works in a pinch. If your using any gasket sealer then only hand tighten bolts. Leave to cure overnight. Tighten bolts in morning. This allows sealer to harden and will not compress once plate is tightened down.