Handyahayden

Hi everyone! I just obtained a 1987 subaru brat 4 speed manual tranny. I found where the dipstick is and checked it...it looks kind of gross...so I took her to a lube place and they said they weren't gonna touch her because she has a "fixed pan" and so they couldn't do a basic drain and fill. My question is: can I add fresh fluid, if so where if not do I even need to fool with the fluid? She has 158,000 miles