Not sure if this is known (not in the wiki) but the heater blower switch can be easily dismantled for inspection and serviced (if appropriate). It has to be removed anyway and since it only takes a few seconds to dismantle well worth checking before buying a replacement.
The switch comprise two parts which can be separated by inserting a small flat bladed screwdriver to ease each side out as shown.
Once separated the switch blade and the contacts can be inspected for surface oxidisation, arcing, etc. Also check the three small springs behind the switch blade are abe to move freely to exert switch blade contact pressure. Quick clean of the contacts and cleaning the 'age hardened' lubrication around the springs and job done - feels right and now works.
Blower Switch by Angelo Evans, on Flickr