Not familiar with the equipment, but all the receivers "Signal Strength" meters I know of just show the receiver-coax-lnb integrity. The Q, or Quality, show the signal from the satellite. Unplug the coax going to the LNB and check the Signal Strength meter. Is it the same as when connected?(unplug the receiver when messing with the LNB coax) If so it may be a problem in the coax. Corroded connector, animal damage, etc. Something broken. Since you said it degraded over months, I lean towards corrosion somewhere. My receiver will show a Signal Strength of 40 with a good LNB(not aimed at a sat) 80+ when the Q meter reads anything(on a satellite), and around 5 or so with no LNB connected.
Another Question, was the original LNB also a Universal? If not, settings have to be changed in the receiver setup.
EDIT-FYI 97W G19 (formerly G25/IA5/T5) I had to remind myself!
EDIT 2 - found and old post(2006) in another forum that says the same- a signal strength of 30 all the time, with that receiver, is coax-lnb integrity problem, check all connectors in the coax run. Confirm the coax integrity.