Similar to how erections are for men, a woman's natural lubrication is frequently a sign of arousal.

Source: https://www.pulse.ng/lifestyle/beauty-health/7-reasons-women-dont-get-wet-even-when-aroused/1s8n8f5

This led us to conclude that the fault was the result of poor lubrication, as a result of degraded engine oil.

Source: https://www.chiangraitimes.com/auto/after-death-bmw-stops-selling-cars/

While you could do the massage without oil, it’s generally recommended that you use some form of lubrication to prevent chaffing and for general comfort.

Source: https://www.huffingtonpost.co.uk/entry/how-to-do-a-perineal-massage_uk_60d356ade4b0c101fc837324