'97 Bonneville SE, 3.8 na, 168k. Replace uim/lim a couple months ago. Been using oil. Removed throttle body to clean IAC & back side of TB & there is oil in the intake. Checked pcv valve at crank end on manifold & it'* bad. I believe this is the cause but wanted to make sure. Also, the fitting on the back of the uim that the large vacuum hose from the booster & a small vacuum hose are attached to--what is is for? Thanks for your help.

The PCV valve is the only place oil can come from in the LIM

Like said, most likely the issue is from the pcv. The only other possibility is the LIM to head bolts seeping. Did you use a little sealer or something on these bolts when you put them back in? The amount of seepage from unsealed bolts should be very very little, they can seep though. My feeling is in agreement that the pcv is the culprit.

The purpose of the large hose is to supply engine vacuum to the brake booster to assist in the power braking.
The little hose is to provide vacuum to your HVAC system in order for it to be able to select the airflow to windshield, vents or floor settings.

Yes, my problem was the PCV. FORGOT TO PUT IT IN! Is there a way to clean up the oil without removing the UIM? There is a thin film of oil that I can see. Not sure if it has puddled in the manifold. Now I'm worried about my cat. conv., o2 sensor.
Also, is there supposed to be a spring with the pcv? The pic in the manual shows one but did some years have them & not others?

Installed pcv valve. Ran some sea foam through the intake. Drove around some and it ran good. Engine light went out! Only problem I noticed is at cruise it seems to surge slightly like it'* wanting to change gears. From what Iv'e read in this forum, it points to a coil going bad. I tested the coils and they are in spec. I'm going to drive it to work this week & see how it runs.

A plug or two may have fouled from the excess oil. You may want to try swapping them out.