My 1990 560SEL with 68k miles has ticking sounds coming from the driver side rear. It occurs when I hit the accelerator and goes away once I gently take my foot off of it. I run Mobil1 15w50 synthetic. I've recently filled the gas tank full with premium along with a bottle of techchron/chevron. After all this, there's still the ticking sound coming. At idle, there's no ticking, it only occurs when revved and I can control the sound as mentioned... but taking my foot off the accelerator. When I give it a nice push on the accelerator, it starts ticking again.

From my description, is this consistant with hydraulic lifters?

If no, what could cause the ticking sound?

If yes, is this a simple fix? What is involved in replacing hydraulic lifters and what tools(special or not) are needed to do the job? If the valve cover is removed, is it required to replace the valve cover gasket with a new one?

TIA