It's a long time ago but IIRC no we didn't see her go to the clinic but we did see the aftermath including Mike finding out what she'd done and given she wanted to save her marriage if she hadn't gone through with it she could have just said so. She was insisting she had terminating the pregnancy and it ended her marriage. There really was no ambiguity at the timme - it was made very clear that she had a termination because her career was taking off and she didn't want to give it up assuming Mike would never find out and when he did after she had done it, he divorced her and kicked her out of the factory (so she lost her job - she'd just started designing) so she had nothing to gain from keeping still being pregnant a secret and everything to lose. Even her father who hated Mike wasn't happy with what she'd done so she left town.

Your right she did have the abortion. Susan didn't want a baby at that stage in her life so she aborted it Mike was furious so ended their marriage. Susan was devastated to have lost Mike and as you said even Ken wasn't happy. She lost everything and left town in shame (months after the abortion at which point she would have a visible bump if still pregnant which she wasn't) she had absolutely nothing to gain by lying about the abortion and keeping the baby. It was a retcon thought up in 2000 having Adam exist in order to give Mike some family with Alma leaving and to have something else for Mike and Ken to feud over.

Well Ken continued to visit Susan (off-screen) since she left after the abortion. In an episode on Christmas 1990 he returned after visiting her in which Adam would of been 2 years old. However he never knew anything about a child in 2001. And I think they also tried to make out he had no contact with her after she left Mike in 1987 which was untrue.

I think that was one of the the first - if not THE first - history changing storylines from Corrie.
Really annoyed me as I remembered watching the old episodes and seeing the abortion episodes.
They tried to say she didn't really have the abortion, but at the time it was what was used to write Susan out cos they sacked the actress.
Susan didn't want to leave Mike, she just wasn't ready to have a baby, so if she'd stayed, it would have been obvious she wasn't still pregnant.
Plus, when you see the episode when she tells Deirdre she had the abortion - and then Mike and he called her a murderer - there's no way she was lying.

Changing history is annoying if you remember watching old episodes, For years and years from when he appeared in 1976, Mike made it clear he was an only child.

Yet 10 years ago it turned out he had an affair with his brother's wife to produce Danny.

Then of course we had Ken's son by Susan Cunningham, when it was obvious Susan, back in 1961 would never have had sex outside of marriage, she was far too proper!
With 60 years to play with I used to dread what they came up with next in the way of history changing!

Yes it was a complete retcon. They did it so Mike and Ken would have something else to fight about a continuation of their lines and no other reason. I've never liked the way they killed off Susan so casually just to introduce Adam who turned out to be a real non character anyway. Though at least he's provided an explanation for Ken's absence this last year! Just what is meant to be wrong with him?