$2500 sounds too low to me for a nice 190D with low miles, especially if the body is good and the interior has held up. Find examples of similar cars that have actually sold, and send them to the insurance company (eBay, this site, other MB sites). Bombard them with info that supports your side. Find similar cars that are actually for sale, and include those.

The longer you hold out, the more likely the ins.co. is to give you a fair value. Their first offer is usually a low-ball to get you to settle quickly at a low price. If you feel like they are not treating you right, call your state's insurance commissioner's office for help. That office may be part of the state attorney general or some other state office. They are the "big stick" that is supposed to help you, the little guy, stand up to the insurance co. I used them once in the past and they immediately got the attention of the insurance co. and got them to deal with me fairly.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC