Lift Pump Filters

Maybe its just me but in my experience the strainer is normally located on the pump suction and the filter after the pump. Placing a filter before the pump requires the pump to draw the fluid thru too great a restriction and could cause cavitation. Strainers are installed to protect the pump from ingesting rocks, bugs, small rodents and such. It would seem that your system is installed in reverse of the normal order.
Your "goop" is probably related to the water contamination and is likly biological in nature. If you do not have a means of eliminating water from you lube system you should have one installed. A centrifuge, coalescer, air stripper or vacuum dehydration system should be standard equipment on all large circulating systems such as your turbine. This system should be in regular use and continuous use if you have chronic water ingression.

Has your craft been using STP for a reassembly lube? STP will collect water and hold it in suspension instead of letting it drop out to the bottom of your reservoir. We have cleaned out a semi clear sludge out of the bottom of our Turbine oil tank and contributed it to the STP we were using. We have stopped using STP for several years and the problem has went away.

Simple test the goop to see what it is and at least do an FTIR and metals. Water can cause deposits so also check your steam turbine oil for water demulsibility and do the rust test as well as the other recommended. Nothing should be added to a steam turbine oil without prior testing and for starts use an ISO VG 1500 or so steam turbine oil. The current formulation of STP has additives in that are good for engine oils but affect the demulsibility so you can end up with more that 100 ppm water in the oil. Also drain off any free water every day from the reservoir and have the operator note how much in the logs.

Ken