Hello and welcome to the forum!
Congrats on your K1000. That is a typical issue with these older cameras. It is usually related to lubrication. The best course of action is to send it to a shop for a CLA (Clean, Lube and Adjust). That will get it back to like new condition and will provide years of enjoyment. I see in your profile you are in the US. I can recommend Phototronic.biz in Kansas and Eric Hendrickson in Tennessee among many others.
Depending on your skills, if you are comfortable with DIY repairs, you can try the following:
First you need to remove the bottom cover of the camera. It is held by 3 screws. You will need a JIS cross point screwdriver for this. Do not use a regular Philips screwdriver.
The bottom of the camera will look similar to this:
Most likely the issue is that the mirror return gear is not completing the cycle when the shutter is fired. Very carefully, apply a tiny drop of very light machine oil to the mirror return gear. Be careful not to put an excessive amount of oil. A drop will do.
Give it a few minutes and start exercising the shutter at different speeds. As the oil slowly makes its way in, it will start to improve. It may take a few hours, sometimes overnight. Exercise the shutter every few minutes.
This may or may not be a permanent solution depending on the condition. A proper CLA will ensure your camera is in top shape for years to come.
Hope this helps! Let us know how it goes and if we can be of further help.
Thanks,
Ismael