Well, this is my problem...

My 2.5 is rattling badly, and it's coming from the timing cover. Also,
until recently there was a metallic knocking coming from the cover.

Now the cover is leaking oil, though the knocking sound has stopped.
Rattling continues. Also, the last couple times I drove it, whenever
out on the highway it would do a sort of surging/lunging...thing while
under a load/at higher speeds. You know, like when you have a bad plug
wire and one or two of the cylinders is firing late/not at all. I
figured that perhaps the teeth on the gears are worn badly enough that
it might have actually...I don't know, jumped a couple teeth, changing
the valve timing. Or something. At this point, I'm not driving the
car.

I've assumed up to this point that the oil leak was caused by the
timing gears wobbling and knocking against the cover, eventually doing
it enough to wear a hole and spring an oil leak...but I've been told
by the mechanic who's going to replace the gears for me that gears
simply can't do that (or at least not these kind of gears), and that
it sounds more like something a chain would do. Also, I just read
elsewhere that this year ('90) they switched to timing chains instead
of gears.

Soooo my question is...how can I tell, beyond a doubt, which I have
without cracking the cover open---gear system or chain system? I've
already purchased gears (%$#^% $140 for a couple of metal cogs), but I
need to know very soon if I need to go ahead and order a chain
instead, so that it's waiting for him once he goes to do the
work...which will hopefully be next Wednesday.

If it IS a chain, can I go ahead and use the gears? They'd make the
camshaft run backwards, eh?