(duplicate thread, my apologies)

JCB, 1550-B. Has two access covers in the front cowling of machine. In my 20 years of owning this machine, I always thought they were simply access holes to the pump for better access. Nope. I now know that the sides of the front are actually the actual hydraulic tanks and these are covers for direct access to the tank and the strainer. (not the filter mind you, the strainer) Well, guess who has gone 20 years not knowing that there was a strainer in there! (#16) So I''ve not got a new strainer in the garage, waiting until this rain stops and I can get this done. I discovered this was a cover to the oil tank when I was whistling dixie.... grabbed an adjustable wrench and started to loosen the bolts that hold it on. FORTUNATELY for me, I didn't get my ratchet or powered tool out. Also, fortunate for me, I was simply cracking them loose in case one was rusted, I didn't want to stop and put them all back. So when the last one loosened up a bit, I started to notice oil seeping out from behind....and THAT is when my lightbulb went off that this was a tank of oil, not an access cover to the pump. Tightened them down and understood what I was up against AND, what I just dodged 20 plus gallons of AW-32 coming out like Niagra Falls on me. This is when I called the dealer and discovered the strainer was in there. He agreed with me that they might recommend it being changed after 20 years of ignorance. Ordered the parts HOWEVER, they do not have the gasket any more....so now I have to find/get/make a gasket. So what I'm wondering is, (ignoring the error of my comment about size) 1. Do I simply go to a hydraulic shop, tell them I need a sheet of gasket material and come home & cut it out? 2. Do I cut a "ring" (cut inner portion out so I have a gasket that is maybe one inch wide and 10 inches diameter) OR, would I just cut the 10" diameter and leave the inner portion. (I hope that makes sense) Interestingly, what caused me to notice this was the site glass is oozing oil a little bit. Not a lot at all, but I don't like it so was looking into that when it snowballed into the screen being added. Would any auto-shop have appropriate gasket material? I've got auto shops 10 miles from me, the nearest hydraulic shop is probably near 40 miles. Side question: Obviously, I've never been inside these hatches. I HAVE drained the oil before and the oil in there is maybe 1 1/2 years old. My question is, should I look around and try to "clean" the inside of this cavity? Of just change screen & close it up? What might I expect to see inside of here (dirt/sediment wise) other than Jimmy Hoffa's body?