Indeed, my W123 is the same way, and I've heard the same: that it's perfectly normal. Holding itself in 1st gear longer helps get tranny warmed up and to optimal operating temperature more quickly.

Of course, as Jackd advises, a fluid and filter change never hurts if it hasn't been done recently.

Regards,
- Ryan

__________________
'95 E420 - 'Shadowfax' 138kmi.
'92 Volvo 740Turbo Bard 193kmi
'74 240D - 'Ol' Green' 4spd Manual 104kmi. (sold )
'77 300D - 'Red' 223kmi (sold)
'75 240D - 'Bianca the Blue Bomber' (sold)