IMO 20-50 is too thick for daily driving use. The thicker oil is going to increase pressure, but at the cost of restricting flow. Your tapping may have gotten worse by oil starving the engine with that 20-50 oil...
Tapping, knocking, ticking, etc. is never "no big deal". That is a sign that something is not adjusted or operating properly. Using thicker oil is nothing more that taking aspirin for a headache; it covers the symptoms. Drain your oil, put something along the lines of a 5-30 or 10-30 oil in the car, and see if the ticking "hopefully" goes back to how it was.
Also, oil in the plug valley is usually caused by leaking valve cover gaskets or a no.3 cylinder head cover gasket (that's a part of the piece that runs the length of the engine over the spark plug valley). Do a quick search on the forum here and you'll find a dozen or so threads on the topic.
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1989 7MGTE R154 Targa Top White Package w/Blue Interior
Driftmotion 57trim CT26, Upgraded Intercooler, 2.25" Hard Pipes, 3" Turbo Back Exhaust with Test Pipe, HKS VPC w/GM 3 bar MAP sensor, APEXi S-AFC, Walbro 255lph fuel pump, ProSport EVO Series Boost / Fuel Pressure / AFR gauges, Lotek a Pillar Gauge Pod, HKS Type 0 Turbo Timer, Eibach Lowering Springs, Tokico Illumina II TEMS struts, custom powder coated Motegi Racing TrakLite wheels
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