Retiring saleman's short trip in car helping to produce sweat (12)

'sweat' is the definition.
(I know that sweat can be written as perspiration)

'retiring saleman's short trip in car helping' is the wordplay.
'retiring' shows that the letters should be reversed in order.
'saleman' becomes 'rep' (I can't justify this - if you can you should believe this answer much more).
'short' means to remove the last letter.
'trip in car' becomes 'spin' (as in taking a car for a spin).
'helping' becomes 'ration' (a ration is a serving or helping).
'rep' back-to-front is 'per'.
'spin' with its last letter removed is 'spi'.
'per'+'spi'+'ration'='PERSPIRATION'

'to produce' acts as a link.

Can you help me to learn more?