550 Fuel tank

Hi , I wonder if anyone else has had fuel tank issues with a 550. With a dead engine and no fuel I opened the tank and saw this. Its like a varnish and hard to remove. Weird rubbery residue . Pumps are gutted. Any suggestions on ho it should be cleaned before putting the replacement pumps. P.S. can the replacement pumps from a 575 be adapted to run in the housing of the 550 Pump. This is the second time its happened in 6 months. Last time I used the Maserati 4200 pump inserts in the 550 housing and it worked fine.
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Many thanks. Will see if its worth removing or if the scaling can be removed by some solvent first. I wonder if its the left over from the fuel pump getting consumed or something to do with fuel being stagnant in the car which has only seen 300 kms of use in 5 years