Does the Linux PPTP server have a route for your subnet via the dynamic connection that is formed? This is going to be tricky. I don't think you are doing to succeed. If the 1941 has a crypto licence I would change over to IPSec. I would use strongswan on the Linux box.
How to set-up PPTP Client on Debian 9 - PRADO May 05, 2018 Connect to a PPTP VPN Server from Ubuntu Linux Dec 02, 2012 VEXXHOST - How To Setup Your Own VPN With PPTP on Linux In order for a client computer to be able to connect to our VPN server, we should install the PPTP client using the following command (the first one is for CentOS, the second is for Debian/Ubuntu): # yum -y install pptp # apt-get install pptp-linux The VPN client request the ppp_mppe module, so we need to load it: # modprobe ppp_mppe [Mikrotik] PPTP VPN server configuration on Mikrotik - YouTube
How to set-up PPTP Client on Debian
Newest 'pptp' Questions - Unix & Linux Stack Exchange
Connect to a PPTP VPN Server from Ubuntu Linux
Newest 'pptp' Questions - Unix & Linux Stack Exchange