Do not try this; I am sure there are better ways out there for most tape problems. I am posting this as it may help with further understanding of underlying issues and precautions.
I have a bubble on the start of a prerecorded tape (I got it for free on top, so no problem here), it lead to dropouts and switching to side B. Playing with a wet felt pad made it a little better, but still dropouts.
I cleaned it with isopropanol on a cotton swab while on top of the felt pad, it left it bent downwards a little. I played it like this, the first times utterly horribly squealing at that spot (stick slip), but after many winding/re-winding attempts, it works so nicely that I can barely see some flickering of the error correction while in service mode.
I also learned that one reason for the gap between the first actual tape segment from the leader and the audio is that if it is damaged somehow, it still can read the fast forward command in the worst case a second later, and it does not matter that much.
What is the worst thing you have done to a tape or a player that solved a problem?
A literal small round bubble on the chrome tape, @AudioGarage and I found them on badly stored blank tapes, this is the first time I saw something like this on a prerecorded tape. I did not take a photo of it unfortunately and I don’t want to search for a spot that plays fine now.
Hi max I have done this similar cleaning process but with additional optic aids. I have explained this to Dr. DCC who has made a youtube video to fix dropouts on prerecorded tape( look for it at DCC Museum youtube page).
You have to use a led light source to located those “spots”," bubbles" or " debries" with a microscope.
Once you locate the affected area clean with iso and cotton bud over the felt pad gently in one direction.
The led light will identify the affected areas more clearly that other light source. I have restored many dcc tapes with this simple method. Hope this helps , Al.
I did it maybe a bit stronger than gently after all it ended up squealing temporarily, maybe less would have been sufficient without this side effect, maybe not it was not a single drop out but multiple caused by the same spot.