The OLAC validator runs off of an unit of software which has the heartbleed security vulnerability. Thinking about implementing a validator the following software comes to mind. https://github.com/zimeon/oaipmh-validator There was also an Online OAI-PMH validator from a former engineer on the Europeana project. I think he is based in Greece. His solution is not open source, but he mentioned that he would consider adding the OLAC profile. https://validator.oaipmh.com/
It would be good to see what other OAI-PMH validators look like and how submitters expect to interact with them.
https://validador.rcaap.pt/validator2/?locale=en
http://oval.base-search.net/
https://doi.org/10.17700/jai.2016.7.1.277
https://rdamsc.bath.ac.uk/msc/t64; https://www.openaire.eu/validator-registration-guide ; https://github.com/EuroCRIS/openaire-cris-validator; https://www.fosteropenscience.eu/content/openaire-compatibility-validator-presentation
http://oai.clarin-pl.eu/