I wouldn't spend the money on a new pump. Rather, remove the solenoid valves and check them out; it's a ten minute job. Parts from Bennitt for the pump are not expensive at all. Quite possibly some contamination got into the system when the second actuators were added and causing the solenoid seats to not seal. Double check there is oil in the hydraulic unit when the tabs are fully deployed; if it is running dry, air will get into the system and the tabs will move with the water flow across them. FYI if the tab actuators leak, they will leak into the water and you will notice in the fluid level dropping in the HPU. Here is a video I found on the solenoid servicing -Thanks for your input. Yes, pump appears ok, or at least everything worked ok when the tabs were the standard size. Issue of blow back only occurred once the tab sizes were increased.
There may be an issue of internal leakage but I am not 100%.
I was wondering if a bigger pump may fix the issue. Or do our boats already have the biggest?
You may be onto something with the poppets. Perhaps I should buy a new pump and see how it goes. If no good then go for the dual option…
// edited to add: a friend with a Maritimo 48 apparently has a similar blow back issue which is strange for a production boat with no modifications//