You have to R&R the intake plenum in order to remove the TB's and get to the rubber mounts. This requires disconnecting the big rubber hose from the AFM in the air-filter, then snipping all the one-time-use Oetiker clamps holding the rubber connectors from the top of the throttle-bodies to the bottom of the intake plenum, then snipping the releasing the clamps on on the top of the actual throttle bodies (generally screw clamps.)
I'd strong suggest replacing ALL the rubber you can while it's apart - so thats 3x the rubber intake to plenum hoses, and 3x the rubber throttle body mounts. Those mounts bolt to the top of the head (try not to drop any parts into the openings while it's apart.) - Make that 4X if you have a K100..
Once all the clamps are off - the intake plenum can be rocked toward you out of the frame. It is VERY tight clearances. Then you can remove the TB assembly by removing the bolts holding the mounts to the head. If you were ever thinking of replacing the throttle cable, or choke cable - there would never be a better time. These both connect to the throttle body assembly. Also a great time to replace the hoses going to the fuel pressure regulator (mounted on the rear of the TB assembly.)
Once you have the TB assembly loose - you can remove the rubber mounts and replace them with new ones. If you have the screw clamps there - you can fasten them to the TB's and then mount them and the TB assembly to the head. If Oetiker clamps were used they can be crimped at this point - AFTER making sure the screw or crimped-ear doesn't interfere with the movement of the TB linkage/butterflies.
When I did mine - many years ago - I used a smear of RTV sealant on the bottom of the mounts. I used electrical grade which does not give off acidic fumes. Since you don't have an O2 sensor to worry about poisoning the RTV works well for this application. Tighten them evenly (there is some torque spec somewhere).
Next put the rubber hoses to the plenum on the top of the TB's - but do NOT crimp the replacement Oetiker clamps (you need them to be able to move a bit) - but DO slide them over the rubber hoses. Use a small smear of silicone based grease on the spigots coming out of the intake plenum, and try to wiggle it back down and into the correct position. Once everything is in place, you can crimp the ears on the Oetiker clamps using Oetiker clamp pliers (they're used on CV joint boots, so your local NAPA dealer will have the tool in stock.) Again - check their orientation to avoid interference with the throttle linkage.
I'd also suggest replacing the O rings on the brass-air-bypass screws, and cleaning those passages with some carb cleaner before reassembly. The stock setting for them is 1 turn out from GENTLY seated. That's a good starting point. If the leak fix was successful you'll find they all pretty much will be open the same amount when you do the idle TB balance.
DO NOT adjust the linkage between the TBs - except the idle screw. The other screws should be painted GREEN or have green/blue caps over them - which in BMW parlance - means LEAVE THEM ALONE.