I believe that the UP2-P pump with PTFE gears (impellers), rated at 10 l/min at 24 volts, part number 16420213, is a good replacement for the Flojet 4105. I believe that the UP2-P 24 volt pump will output about 5 liter/min when connected to 12 volts and draw about 1.5 amps. To expand on Scott's statement about replacing brushes, Marco part number R6400080 (R-KIT motor cap ø52 mm) costs 24.93€ from www.Marco.it, or $28.56 from www.marco-pumps.com (more about this source below). This motor cap has the brushes installed. I believe that the best process is to simply replace this cap (photo below).The more adventurous could probably find and solder brushes to the existing cap.

There is another source for Marco Pumps, shipping Marco pumps, worldwide from Vienna: www.marco-pumps.com  You will find almost all Marco pumps at this site (soon to be 100% of them), and a huge selection of Marco Pump Parts (Spares and Accessories). This source regularly ships to all of Europe AND is especially good for shipping to the USA, because they have a flat rate of $15 to ship to the US via USPS. They are now one of about 25 of the Preferred Vendors to Amel Yacht Owners School. The Preferred Vendor Discounts range from 5% to 20% on Amel OEM parts, equivatents, and services. 

I will share the Preferred Vendor Discount code for Yacht School clients with www.marco-pumps.com.  I have never done this before in this group. The Preferred Vender codes have always only been available to my clients, but I will make the exception this time. If you choose to order from www.marco-pumps.com, use code AMELSCHOOL to receive an additional 5%. Frankly, it appears that www.marco-pumps.com may be the best place to buy Marco Pump Parts (Spares and Accessories). They appear to stock a wider variety than www.Marco.it or the Marco US distributor www.mate-usa.com

DISCLAIMERS: 

I receive absolutely nothing when my clients order from Preferred Vendors. 

We do not have much history or experience with www.marco-pumps.com. At this point, I know of only one Amel owner who has ordered from them.