94 with problems

I seem to have a whole bunch of problems with my 94 limited edition 4 cylinder jetta.

my mpg have spiked, over the course of one fill up, i typically get 400 miles to the tank, then all of a sudden im only getting 330 miles to the tank. thats 30mpg to 25mpg

also, my dipstick funnel shattered, (this also happend to my friends jetta, how commen is this?) and a small piece of plastic fell down the funnel, what is this going to do?
this happened about 3 tanks before the mileage spike

problem three is a rattle, it sounds like its comming from arround the transmission area, its definatly an engine/exhaust sound, its rev sensitive, and it seems to peak around 2800 rpm. this sound has slowly gotten louder since ive had the

the last problem is sunroof related. my sun roof tracks broke, so i pick up some used but working ones. they work fine, but the button commands dont work right, if i push forward for close, it closes all but 2 inches, and wont go any further. then if you want to crack the sunroof, by pushing up, then it closes the last 2 inches, but doesnt crack. then when i lock teh doors from outside and the sun roof SHOULD automatically close, it then cracks it those 2 inches. its acting like the buttons give the wrong commands.
did i need to reset anything? is there a special position i should have it in when i install it?

can anyone help my ailing vw?

The piece of plastic may have entered the oil pan. Change your oil and see if there a plastic piece comes out.
Drastic drop in gas mileage can be a number of factors.