yea i cleaned all earths as part of service, including the ems2 one. all other readings seems fine so didn't think would be earth but cleaned anyway. my sender unit is the large greyish one like you say but it doesn't have the m4 bolt but rather a spade terminal coming out of it. cleaned that too. i think my readings are due to possible gunk moving around and partially blocking the sensor hole, or just oil viscosity like you say. seems to have settled a bit in the last day or two. sometimes when i turned the engine off, instead of the low pressure warning going off it would stay on about 30psi or it would drop down to 3 or 4 and then spike back up to 30ish. then the next time you start the car it would idle at 84 (30+54). maybe didn't reset itself properly. just a nuisance more than anything. i think high pressure is erratic reading but lower pressure is what you need to look out for. im pretty confident it would let me know or i would notice as i'm on gauges like a hawk.

