Oil pressure problem and open gasket?

So I recently noticed that under the passenger seat of my 87 LE van that an orangey transparent fluid has been dripping on my garage floor.. Almost near the front passenger wheel but to the left of it. (Directly under passenger seat)

For all the care that my van needs I take the van to a local mechanic that has worked on my van for the past 3 or so years

The mechanic said that the oil pressure sensor needs to get replaced and that I need to replace the "open gasket" (not sure if that's a part or if it's the correct name?) he has offered to do it for me for $200 since he did explain he did need to do quite a lot of work to get to the problem and get it fixed.

Or or is he really over pricing me?

When it comes to my van I never do any services to it. Although I know I should I just haven't so far.

any help or responses are appreciated!

Perhaps he meant the oil pan gasket. FYI these vans don't have oil pan gaskets (although I've seen aftermarket ones before). Toyota just squirts a bead of FIPG sealer around the periphery of the block then squish the oil pan into it. I've rebuilt a few of these engines and I do it the same as Toyota (so far I've had good results). If it is the oil pan gasket, it sounds like a good deal. Tim

If these vans don't have oil pan gaskets then what else could he mean?

Edit: he did mean oil pan gasket. Auto zone sells them for about $10 and the oil pressure switch for about $10 also. I'm gonna take it to him and have him get it done! He did mention that at a mechanic shop they charge about $350 to do this job