You want to use Roland cleaning solution. Like from here.
CLEANING(ESL5) 500ML
I would recommend converting it to a SP300v and then you can use the more modern rip versaworks. To convert it you basically will flip jumpers or dip switches on the board and then you will be all set to run versaworks.
To soak sp300/sp540 print heads (this is the quick version)..
Do a manual cleaning...while the head is at the other end of the printer clean your capping station...then using a binder clip or something like it clamp the hoses that go from the captops to the waste ink bottle...then put some cleaning fluid in the cap top and put the print head back over the cap top and (with all power off) manually raise the captops to the heads and leave it for xx time and then let the printer do a normal cleaning...
I DEFINITELY LEFT OUT SOME STEPS....LOOK ONLINE FOR DETAILED STEPS.
Having told you the above....here is what i have done with great results on many Roland printers over the years.
Manually clean the heads
Soak a swab in cleaning fluid and carefully and lightly push it against the head (do not rub).
Clean the capping station area, put new wippers on and a wiper scrapper and REPLACE the captops.
Let it do its normal its usual steps after you have done the manual cleaning (dose a few things then shuts off the printer).
Turn if back on and let it do its normal cleaning cycle...
Then do a test print...assuming it is not good yet (keep to compare later prints) do a normal cleaning by selecting it from the menu...then do it again, and again, and then do a test print...compare to the prev one. If it is not good but have gotten any nozzels back repeat the cleanings from the menu and do a 3rd test print.
If still bad but nozzles are coming back, keep doing it but do a manual cleaning about ever 3rd or 4th cycle.
I have brought back heads that didn't fire any nozzles back to 99% (which is plenty for quality prints) in the mater of hours or at worse a day or two.
ALSO USE ROLAND INK...dont use aftermarket.
