Again transfer case switch failed

Blazer LT -98 vacuum lines again filled with automatic tranny oil. I guess transfer case switch failed again. I changed it just 1,5 years ago. I red somewhere that GM has changed this switch better one..? In Rockauto.com they sell two different switches: Dorman part #49315 and #600500. Which one is better? Should I also replace vacuum switch over the intake manifold or clean it?
Thanks,

Your problem is not the switch. The seal between the transfer case and the transmission has failed allowing transmission fluid to leak out of the transmission into the transfer case, a common problem. Low fluid in the transmission will lead to failure and expensive repairs. I would suggest that you get that seal replaced.

But... inside transfer case there is automatic transmission oil. My problem is that vacuum lines connected to transfer case switch are filled with oil. So the switch itself is leaking oil...

As said.
Can be caused by over filled transfer case.
Check the fluid level in it and trasmission.

Right, transmission fluid in transfer case AND in transmission. The only seperation between the fluid in the transmission and the transfer case is a double lipped seal on the transfer case.

Yes... you were so right. I opened transfer case filling plug and out came lot of oil..
Next task is to drop transfer case and change this seal. What else should I check or repair when it's down?
After replacing seal should I clean vacuum lines? Heater is now blowing only from top ventilators, guess it doesn't get enough vacuum to operate::?
Thanks,

After replacing seal should I clean vacuum lines? Heater is now blowing only from top ventilators, guess it doesn't get enough vacuum to operate::?
Thanks,

You are right, oil in the lines not allowing the selector to work properly. Only way to fix it is to get those lines cleaned.

In transfer case there is input shaft seal, but does tranny have output shaft seal and if, do I have to replace it?
How should I clean vacuum lines? Which vacuum lines need to be cleaned? Is there any diagrams from vacuum lines available?

The seal is in the transfer case input shaft collar.
It is a double seal setup that seals fluid both ways.
Check with dealer on seal or seals.
May be a one piece double seal or two seal.
If the two seals stack one one way and the other the other way.

On vacuum diagram check under hood.
A factory repair manual or all data sub has the vacuum diagrams.
http://www.alldata.com/products/diy/index.html
Also AZ web site and a lot of public libraries gave care repair info.
If vacuum line re very bad or swelled up bad replace them.
Let us know how it goes.
Good luck

If you do it yourself you will need the case gasket that goes between the transfer case and the transmission. The input shaft seal is a single double lipped unit available from the dealer for about $12.00. It is tricky prying the plate off the xfer case that houses the seal. It is sealed with RTV and no apparent place to pry it off. IF you look really closely you will find a couple of little indentations where you can use a screwdriver to pry it off. It's tough. You will need some new RTV to seal it back on. A pretty messy job without the right tools, etc. Might be worth having a transmission shop handle. Good luck with it.

OK, thanks for your help. I'll let you know how did it go...

You are welcome.
And remember when the transfer ase is overfilling the transmission is getting low.
Keep the transmission fluid checked.
Good Luck