I see that a Swiss 1881 cover is being auctioned by Jean-Paul Bach
AG of Basel, addressed to “Monsieur John Büttikofer, Esq.” at the “Dutsch factorey” in Monrovia.
In case there are members whose commitment and pockets are deeper than mine, I thought you might be interested: minimum bid is CHF 1,800++.
I take it that this is Johann Büttikofer (1850 – 1927), the Swiss zoologist who wrote
Reisebilder aus Liberia (Leiden: E. J. Brill; 1890). Büttikofer worked in Rotterdam, wrote the book in Dutch, and since his Dutch-sponsored first expedition spanned 1879-82, this appears to fit.
Are covers to Büttikofer commonly found?

Comments
I wasn't aware the Dutch had a presence in Liberia at that time but apparently the "factory" word was used to indicate a trading post or warehouse rather than in the Western senses of being somewhere where products are manufactured.
The Dutch it appears had several such factories on the coast
PS I won't be bidding on the cover!
These offices were administrative locations for many different types of colonial economic endeavours such as plantations, etc (ie, coffee, rice, whatever). These were spread throughout the Dutch colonies such as Indonesia. Even though the Dutch didn't colonize Liberia, they had a presence.
The Dutch had a long, early history in Liberia, well before American settlers.
https://liberiapastandpresent.org/Netherlands/Overview.htm
People sent mail to these established offices to be picked up. People sent mail to their country's Consul as well. It was an easy and unambiguous way to send mail.
I have an 1881 Swiss Buttikofer cover. I have 2 covers to A. Veldkamp, from Leiden and Groningen, Netherlands. One sent to Dutch Factorij and one sent to the Dutch Consul (1888/1889). He was a zoologist!
Thanks, Martin, for the Buttikofer information and sending me down a rabbit hole. I got me reaching out to my fellow Dutch Indonesia collectors...