sadly I crashed A LITTLE LESS THAN A YEAR AGO,( SOME ONE PULLED IN FRONT OF ME) TOOK THIS TIME TO RECOVER( SOME BROCKEN BONES)
AND NOW I NEED TO REPLACE MY UPPER FAIRING OR COWL ,could you fellows tell me if the same part from a Lt will fit RTs. thanks

As far as I know, the main part of the upper fairing is the same for both models.  The difference being the amount of other stuff(dash panels, map lights, power windshields, radios, etc.) that was loaded into the space behind the windshield.

K100RT and K100LT fairings are the same. I have both and the painted parts and brackets all same, including mirrors and mirror pods. The black leg panels some have slots in them some don't but they are interchangeable as well. So too are the storage boxes and lids. And screens even though some different shapes the screw holes etc are same.

Good to see you getting back in action too.

As PointSevenFive said the top panel, if you have the extra temp and fuel gauges, this panel may differ.

The lower one under the mirrors and below the screen is the same one, holes are cut into it on the LT for the gauges or speakers and the cut positions are actually marked out on the back.

The K75RT fairing is also same on the painted parts.

I would guess that with the way BMW did things on the K bikes, all your internal trim parts will fit in any LT/RT upper fairing. 

If the bike went down hard, the mount for the upper fairing may be a bit "tweaked".  I dropped mine last summer on a muddy shoulder and the fairing was pushed over about 3/4" from the centerline of the bike. 

I made a simple jig to straighten the mount rather than taking a chance on getting another bent one on the used market.  If you need it, I can give you some direction on building the jig and straightening the mount.

The K100LT upper fairing also has flip open air vents built into the fairing located at the rear corners.  K1100LT's and K75/K100RT's do not have this opening cut into them. See part no. 2 in this diagram.

http://www.realoem.com/bmw/enUS/showparts?id=0516-USA-03-1991-K589-BMW-K_100_LT_87_0506,0516_&diagId=51_0067

Ken 52 - as all the others have said - the RT & LT upper fairing is interchangeable. 

Following my wreck last year on one of my LTs (someone pulled out in front of me, the sudden stop also resulting in broken bike and broken bones) - I rebuilt the bike using a RT upper fairing that I picked up off eBay (in very good condition from a cafe sacrifice). I considered cutting holes in the "new" fairing so that I could fit the vent flaps (from the broken upper fairing), but in the end decided that I didn't want to. I am not sure how much difference the vents really make and it seldom gets that hot here in the UK to warrant them. It wouldn't be a hard job to do though, if you take a template from your old fairing and do some careful drilling, dremmelling, cutting and filing. When I got my eBay fairing, I also got the mount with it - like point7-5 says, a hard knock does cause the mount to bend and mine was definitely twisted out of shape.

Good to hear you're making a recovery and getting your bike fixed.

Ken, I have the upper/main fairing from a 1985 K100RT if you are interested.  Bonus is that I'm in Corvallis, OR, only a few hours away from you, so it would not be too hard for you to collect it at my place.  Free of charge if you come and get it...I'd be glad just to get it out of my garage.  PM me if you are interested and we can set it up.

Those main fairing body side vents did come on some K75RTs. My 90 had them. (And I know it was from the factory that way because it was in mint condition with only 6,700 miles when I bought it.)

The interior panels from a K1100LT won't fit a K100RT/LT because they moved the fairing a little forward on the K1100LT. 

But the main fairing body is the same across all RT/LT models.